Extrusion Blow Molding

Part Design Contest

Plastic Blank Firing Cartridge 5.56 x 45 mm NATO

Penn State Behrend - Plastics Engineering Technology

Michael Rossi

Jacob Tingley

Date: 4/20/2018

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Table of Contents

1. Abstract

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2. Design Details

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3. Mold and Tooling Details

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4. Manufacturing Details

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5. Design Drawings

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6. References

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7. Appendix

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ABSTRACT

The objective of this project is to design an extrusion blow molded alternative to both standard M200 brass blank cartridges and injection molded plastic blank cartridges. Militaries around the world utilize brass simulation rounds to enhance combat training exercises. For simplicity, this project will focus on the U.S. Army’s standard 5.56 mm x 45 mm M200 blank cartridge. These rounds are notorious for causing weapon malfunctions and drastically increasing the amount of maintenance required for proper function. The malfunctions occur largely due to the shape of the M200 cartridge, which lacks the distinctive angled tip of a bullet, preventing the round from being chambered properly. The primary reason the round fails to eject is due to the accelerated buildup of residue in the chamber. Aside from functionality issues, the brass shells also present logistical challenges. After firing, the shells must be collected to prevent civilians from entering firing areas and collecting the shells for reloading. This action also cuts into training time, and requires Army leadership to accommodate valuable training time for brass recovery.

Plastic blank cartridges were first developed by the U.S. Army in 1974 in order to address issues associated with brass cartridges, as well as reduce production cost. They were injection molded using polycarbonate (Lexan 191). Several issues arose with the cartridges cracking along weld lines and poor gate placement. The final product demonstrated that plastic cartridges were feasible replacements for brass cartridges. However, the U.S. Army still almost exclusively uses brass cartridges during field training. Some plastic cartridges are used, however, soldiers prefer the use of brass due to the higher frequency of failures experienced with the new yellow plastic blanks.

The shape of standard 5.56 mm x 45mm ammunition and its inherent requirement of being hollow makes it a perfect candidate for blow molding. It is speculated that many of the flaws associated with current plastic cartridges are a result of being injection molded. One of the struggles of the U.S. Army’s 1974 project was the immense internal pressure build up and resulting outward force caused by igniting the gunpowder contained within the part. Their parts would rupture along weld lines. Blow molding affords the opportunity to orient the material towards the centerline of the part, thus improving the part’s resistance to the internal pressures. The most likely reason that plastic blanks are not already

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blow molded is simple lack of interest on the account of the U.S. Army, due to old fashioned misconceptions of plastic’s feasibility, lack of knowledge in the plastics field, and its previous failed attempt with injection molded blank cartridges

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DESIGN DETAILS

Introduction:

The part is a standard 5.56 mm x 45 mm NATO cartridge adapted to plastic part design guidelines. The head of the part (1) was rounded and designed to encourage the part to rupture along the thin sections to allow pressure to escape in a controlled fashion. The neck of the part (2) was modified to remove sharp corners to improve plastic flow and minimize stress concentrations. The primer (3) is not plastic, and will be insert molded, with the material shrinking onto the insert. The wall thickness along the surface of the part was reduced every 90° to encourage the part to split in a controlled fashion. (4).

Figure 1 – Cartridge Components

Blow Molding Application:

Ammunition must inherently be hollow to allow the cartridge to be filled with gunpowder. A blank cartridge is a perfect candidate for blow molding, as they must also be hollow for filling gunpowder. Rather than leaving one end open for the insertion of the lead bullet, a blank can be molded as part of the cartridge, since blank rounds do not fire a projectile. This allows a plastic blank cartridge to perform closer to a live cartridge than the standard M200 blank cartridge, which has a stub nose and often feeds improperly as a result. Also, the ease of insert molding in blow molding allows the primer insert to be molded into the part, taking a step out of the assembly process and one of the major issues with injection molded plastic blank cartridges. Finally, the shape of a cartridge is very similar to that of a bottle, which is a perfect part for blow molding.

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Design Details:

Figure 2 – Standard Cartridge Dimensions

Figure 2 is the detail drawing for a standard 5.56 mm X 45 mm NATO cartridge. The critical dimensions that the plastic cartridge needs to mimic are H1, H2, and P2. These are the areas that must be in contact with the weapon’s barrel in order to constrain the cartridge and allow the weapon to function properly. Additional critical dimensions are L3 and L6, which are critical because they ensure the cartridge will fit properly into the magazine. They also ensure the cartridge’s primer is located correctly for the firing pin to strike it, as well as for the extractor bolt to grab and remove the spent cartridge.

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Design Details: (cont’d)

Figure 3 – Plastic Blank Cartridge Overall Dimensions

When adapting the brass cartridge to a blow molded cartridge, several modifications needed to be made to the dimensions and the part to ensure functionality. The general rule for inside radii is ½ Wall Thickness. With a calculated wall thickness of 1mm, an inside radius of 0.50 was originally applied. According to GE Plastics’ blow molding design guide the smallest attainable radii is 0.51 mm. Therefore, the inside radius was adjusted to 0.60 mm to improve the flow characteristics at the rounds. It may be necessary to use a chamfer instead of a radius should simulation identify the rounds as negatively affecting the desired blow ratio of 0.5.

GE Plastics’ guide explains that for a simple flat panel design that the practical location for the parting line is the center axis of the part. Therefore, the parting line of the part was quickly identified as the center of the part, since the cartridge is a simple flat panel design. A flat wall is required for this part because the specifications dictate that the cartridge have the same dimensions as a standard M200 blank ammunition. Otherwise, the cartridge would succumb to feeding and extracting issues.

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Design Details: (cont’d)

The material selection matrix was driven by the U.S. Army requirements for a plastic injection molded blank cartridge from 1971. While the report and the desired outcomes are dated, they still apply today as the U.S. Army still uses the same M190 Ball cartridge. Figures 4 and 5 are the U.S. Army requirements for the part from 1971.

(Figure 4)

Figure 4 Figure 5

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Design Details: (cont’d)

After consulting an expert in Strengths of Materials, it was determined that the primary area of concern was the 90° sections, which will be referred to as “petals”, on the tip of the part that are designed to bend outwards under loading and allow the pressure to escape down the barrel. Should a petal become dislodged and shot down the barrel, it presents a safety hazard to the user and will prevent the weapon from completing its cycle.

Since the part is a one-time use part, the Ultimate Tensile Strength of the selected material needed to meet or exceed the tensile stress calculated at the section. After performing hand calculations and reviewing them multiple times, it was determined that a wall thickness of 1 mm would be sufficient to prevent the petals from breaking off. Figure 6 below contains the hand calculations, and Figure 7 contains the same calculations using Microsoft Excel to verify the hand calculations.

The value for Pressure was determined through extensive research into the function of an M16 rifle. It was found that 82.74 MPa of pressure is required by the gas tube in order to accumulate enough pressure to assist the recoil-absorption system found in the rifle’s buffer tube. In other words, in order for the rifle to cycle the next round, 82.74 MPa is required. When loading a standard live M855 cartridge, 62 grains of powder are used. When loading a standard M200 blank round, only 6 grains of powder are required. The low amount still allows the rifle to function because a Blank Firing Adapter is mounted to the end of the muzzle to redirect the pressure into the gas tube. Since 62 grains of powder generate all the required pressure and then some, (358.52738 MPa), and 6 grains also generates the required pressure, it was determined that the blank cartridge must internally generate at least 8.001 MPa in order to fire the weapon.

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Design Details: (cont’d)

Figure 6 below shows the hand calculations for determining the part’s wall thickness.

Figure 6

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Design Details: (cont’d)

Figure 7 is the optimal wall thickness calculation from excel, which confirms the results of the hand calculations.

Figure 7

Figure 8, below, is the Material Matrix generated from the U.S. Army’s specifications and desires.

Figure 8

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Design Details: (cont’d)

Figure 9

Bayblend T85 PC+ABS Blend

The Bayblend T85 from Covestro is a non-reinforced PC+ABS amorphous thermoplastic blend. These materials are known for their combination of toughness, rigidity, and flowability. This particular blend of material is available in a wide range of opaque colors as well as in its natural form. In addition to the properties listed, this blend also boasts a heat resistance ranging from 120 °C to 131 °C.

This blend of material was because is blow moldable and meets the requirements set by the US Army for a plastic 5.56mm blank cartridge. This blend also allows the parts to be colored, which can be useful for distinguishing the blank cartridges from live ammunition. This introduces the possibility to color code cartridges according to their caliber to further reduce the chance of misidentification. As an amorphous material, PC/ABS has a naturally higher dimensional stability immediately after molding, and due to the benzene rings found in Polycarbonate, it has exceptional dimensional stability over time. Both properties are crucial in maintaining the part’s tolerances in the field. The impact strength of the PC/ABS blend is critical in ensuring the parts can be transported and airdropped without fear of cracking the cartridge wall, which would be hazardous to the user.

The material’s Material Safety Data Sheet can be found in Appendix 1 and 2.

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ANSYS 18.2 Workbench Analysis:

Meshing:

The rifle barrel was modeled to visually represent how the cartridge will sit in the rifle’s barrel when loaded. In Creo Parametric 4.0 the assembly was modeled so that when imported to ANSYS, the program could generate “Contact” elements to bond the two parts together. The head of the cartridge remains free to move once loaded. Due to the small size of the part and the roundness of the models, a fine mesh was used to properly represent them during the program’s calculations. Figures 10 and 11 below depict the barrel and the cartridge separately. Figure 12 depicts them together. Together, there is a total of 196,660 nodes and 128,752 elements.

Figure 10 - Mesh Plot - Rifle Barrel

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Meshing: (cont’d)

Figure 11 - Mesh Plot - Neck/Head of Round

Figure 12 - Mesh Plot - Assembled

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Loading:

The model was loaded under the constraints depicted in Figure 13. By applying the internal pressure to the entire internal surface, a more realistic result can be obtained than the hand calculations. The hand calculation placed all of the pressure on the tip of the cartridge. By expanding the affected surface, a significant amount of pressure is transferred to the barrel’s walls before the pressure reaches the tip of the cartridge.

Figure 13 - Structural Loading on Model

Results:

The ANSYS package available is unable to calculate the tearing of models under stress. In order to still evaluate if the cartridge’s petals will properly deflect without tearing several variations were run to determine if it would tear.

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First Attempt:

The first model tested included the rounds on the surface of the cartridge. These fillets prevented the entire cartridge from being in contact with the barrel save for the tip. The results are below in Figures 14 and 15. These results generated numbers that made it clear that the lower portion of the part would not fail in shear, as it did not exceed the calculated 65.845 MPa. However, these results are skewed, as the barrel absorbed most of the pressure. Also, since part had room to expand, it did so. It is probable that this would result in the cartridge being unable to eject from the barrel after firing. A redesign was required.

Figure 14 - Deflection Plot - Cartridge

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First Attempt: (cont’d)

Figure 15 - Equivalent Stress Plot - Cartridge

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Second Attempt:

The second model tested did not include the rounds on the surface of the cartridge. The assembly bonded perfectly, with only the tip left unbonded and free to deflect. This model more accurately tested the wall thickness of the part at the tip, and confirmed that a 1 mm wall thickness would in fact be suitable for this application. This is known because maximum stress experienced by the tip was 62.834 MPa. This is very close to the hand calculated result. It is probable that this result is lower because the barrel absorbed some of the pressure, as well as the material itself, which was able to compress closer to the barrel. Figure 16 below depicts the Equivalent Stresses experienced by the cartridge under 6.67 MPa of pressure.

Figure 16 - Equivalent Stress Plot - Redesigned Cartridge

The maximum deflection occurs exactly where predicted, at the tip of the cartridge. The max deflection predicted by the hand calculations was 0.68 mm. The FEA result was even lower, with a deflection of 0.048 mm at the tip of the cartridge. Figure 17 below illustrates the deformation. By observing the contours on the plot, it is clear the cartridge will deform as designed, similarly to the opening of a flower.

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Second Attempt: (cont’d)

Figure 17 - Deflection Plot - Redesigned Cartridge

From the second attempt, it was confirmed that further adjustments to the part’s wall thickness or design would not be necessary.

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Polyflow:

To evaluate the performance of the parison in the mold, a Polyflow analysis was conducted. First the parison and mold surfaces were imported into DesignModeler. Figure 18 below is the imported geometry. Second, the surfaces were meshed. The final mesh had a total of 1,261 nodes and 1,193 elements. The mesh is illustrated in Figure 19.

Figure 18 - Imported Geometry - Parison and Mold

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Polyflow: (cont’d)

Figure 19 - Mesh Plot - Parison and Mold

After setting up the model for Polyflow, two analysis were run. First the “mold close” stage of the blow molding process was evaluated. This includes simulating the extrusion of the parison, the effects of the parison’s own weight and gravity, and finally the effects of the parison being pinched off by the mold surface. The mold closing stage occurred between 0 and 0.25 seconds after the parison was fully extruded. The results are depicted in Figure 20.

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Polyflow: (cont’d)

Figure 20 - Mold Close - Parison Thickness Plot

Using the results generated from the mold closing analysis the “blowing” stage of the blow molding process was simulated. This stage occurred between 0.25 seconds and 3 seconds. After a successful simulation, thickness and area stretch plots were generated to visualize and evaluate the results of the blowing stage. Upon review, it is clear that the parison thickness is appropriate for the part, and it is probable that the part can be blown in reality. Originally there was concern that the cartridge’s small rounds would be too small for the already low wall thickness to conform too without creating thin areas in the part which would fail prematurely during use. Figures 21 and 22 illustrate the results of the blowing stage of the Polyflow simulation.

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Polyflow: (cont’d)

Figure 21 - Parison Blow - Area Stretch Plot

Figure 22 - Parison Blow - Parison Thickness Plot

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MOLD AND TOOLING DETAILS

Mold Details:

Figure 23 below is a colored detail drawing of the B half of the mold. The only difference between the two halves is that the B half has vent lands and channels. Balloons 1 through 6 indicate the location of major parts of the blank rifle cartridge. In order, the balloons indicate; the head, neck, shoulder, panel, chime, and brass insert. The colors also correspond to critical design elements of the mold. The dark blue indicates the parting surface. The light green indicates the pinch off. The red indicates the blow pin hole. The gray indicates the vents. The rest of the colors indicate the same parts as their respective balloons.

Figure 23 - Colored Detail Drawing of B Half

Parting Line:

The inserts have a flat parting line. This was done to reduce the complexity of the mold design process, which reduces tooling cost.

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Venting:

The addition of vents to a blow mold is necessary to allow air to escape when the mold is closed, preventing the visual defects that result from trapped air. These defects include air bubbles and burns. Neither of which are acceptable in this project’s application. For this mold they were placed along the “panel” of the cavity. This method of venting is called parting line venting. The vents were dimensioned to the smallest acceptable values to account for the small size of the part.

Depth and width values were obtained from the Elastomer Part and Mold Design Guide. Four 1 mm-wide channels were added to carry the air from the vent lands to the atmosphere. Figure 24 below is a detail drawing of the B half with dimensions for the vents and pinch off. Detail A and the top view contain the dimensions for the vents.

Figure 24 - Detail Drawing of B Half of Mold

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Mold Details: (cont’d)

Pinch off:

The pinch off is critical to successful blow mold design. When properly designed and placed, it can minimize the flash present on the final part. Despite being a one time use product, the presence of flash on the head of the cartridge could lead to difficulty feeding and/or loading into the rifle’s breach and magazine. The dimensions for the pinch off were derived from the Elastomer Part and Mold Design Guide. The exact dimensions are annotated in the top view and Detail View B in Figure 24 above.

Draft:

Draft is added to the walls of blow molded parts to allow the part to be easily removed from the mold. Since the blank cartridge is a round part, no draft was added.

Blow Pin Hole:

The blow pin hole is located on the outer edge of the mold, and is designed to accommodate the blow pin and mechanism which will place the brass insert into the mold. Dimensions came from the Elastomer Blow Molding Design Guideline, and can be found in the Top View in Figure 24 above.

Surface Finish:

The desired surface finish for the blank cartridge was for it to remain smooth to aid in feeding through the magazine as well as ejection from the rifle after it is fired. The surface finish of the round must be similar to that of a standard brass casing in order to ensure that it performs in a similar manner. The surface finish will have a B-1 level using 600 grit sandpaper, which is typical of parts with a medium polish.

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Cooling Lines:

Cooling lines are crucial for cooling the part quickly to maintain tolerances. Both halves of the mold have had a series-type cooling circuit added. The small size of the mold makes adding a parallel circuit unnecessary, and would increase costs. Figure 25 below is a detail drawing dimensioning the cooling line circuit in the B half of the mold.

Figure 25 - Water Line Dimensions

Parison Programming:

Parison Programming enables designers to alternate the wall thickness of the parison by changing the distance between the die and mandrel as material is extruded. Parison programming is most commonly used to counter the effects of gravity. As the parison is extruded, the material will sag under its own weight. This causes the material to thin as it is pulled apart by gravity. For this project, the effect of gravity on wall thickness variation will be minimal due to the small size of the parison. Also, wall thickness variation is only a major concern about the head of the part. (Purple area in Figure 23). Maintaining a minimum of 1 mm of wall thickness is critical to ensuring the head does not shear off and fire down the barrel with the escaping gas from the inside of the part. Unless later simulations indicate a need to adjust the thickness of the parison to account for parison sag, this project will not utilize parison programming.

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Parison Profile:

Blow Ratio:

Figure 26 below details the anticipated Area Stretch Plot of the parison. The x-axis represents the distance the parison has traveled in the z-direction (as it is extruded down) and the y-axis represents the anticipated thickness of the part. Detailed on the graph are the names and locations of key parts of the final part.

Figure 26 - Predicted Area Stretch Plot

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Tooling Details:

Mold Material Selection:

Aluminum 7075-T6 was selected as the material for the mold. While uncommon in injection molding because of the high pressures, aluminum is the most common material for blow molding. Aluminum has both the highest machinability and the lowest cost, and according to the Elastomer Part and Mold Design Guide is the, “material of choice for extrusion blow molding.” Aluminum 7075-T6 also has a thermal coefficient of conductivity of 167 W/m*K; four times greater than standard P-20 steel. This indicates that Al 7075-T6 is capable of cooling the part four times faster than steel, significantly reducing the overall cycle time. Overall, Aluminum 7075-T6 was selected to minimize costs while also ensuring efficient cooling of the part.

Mold Construction Method:

There are two primary methods for constructing aluminum blow molds, casting and machining. Cast aluminum is commonly used to provide a sample of what the product will be once a machined aluminum mold has been made. Casting yields a mold which is softer and less durable than a mold machined out of a larger block of material. Cast molds are also appropriate for large parts or parts that are being produced at a low rate. With this knowledge, a cast mold will not do for this project. The cost of machined mold depends on the size and complexity of the design. For this project, the cost will be low because of the small size and low complexity. Also, since this is a high production volume part, the harder material available through machining is required to account for wear and tear.

Die and Mandrel:

Due to the small parison required to make the cartridge, a converging die and mandrel was selected. A converging die is used for smaller parts with a diameter of 5 inches or less. This type of die will allow for more consistent tooling temperatures. No extra die shaping is necessary due to the fact that the cartridge is a cylindrical part with uniform wall thickness. The design for the die and mandrel created is based off of information found in the Chevron Phillips Die Shaping for Extrusion Blow Molding.

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Tooling Details: (cont’d)

Die and Mandrel: (cont’d)

Figure 27 below shows a basic design for the die and mandrel that will be used to create the parison for this project.

Figure 27 - Die and Mandrel Design

Mold and Tooling Cost Analysis:

Through an analysis performed in Mathcad, the total cost for all six inserts was determined to be $99.24. While it seems low, the incredibly small size of the inserts compared to most parts and use of aluminum instead of steel significantly reduces the cost. The calculations are based off Chapter 3 from “Injection Mold Design Engineering” by David O. Kazmer. See Appendix for Mathcad calculations.

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MANUFACTURING DETAILS

Manufacturing Details:

This project will utilize Extrusion Blow Molding (EBM) to mold the part as a single layer with mold insert. Extrusion Blow Molding was selected over other processes because it allows the entire part to be molded in one step, with minimal post processing required. EBM also has significantly lower molding pressures than other processes, enabling the brass insert to be easily molded into the part. The lower pressures also allow for the use of aluminum molds. Aluminum has several advantages over conventional steel molds used for injection molding. Aluminum material is significantly less expensive. It is easier to machine, which reduces machining costs. Also, aluminum is much better at conducting heat than steel, which allows parts to cool faster. This is doubly important because of the high temperatures required to mold Polycarbonate, and the need to cool the parts quickly to maintain tolerances. Injection Blow Molding was not selected due to the complexity of molding a preform for such a small part. At that point, it would be more logical to simply use Injection Molding. However, Injection Molding would drastically increase the overall cost. Not only are Injection Molding machines more expensive, they also require more energy to operate and the tooling and machining costs for their molds are much more expensive than Blow Molding machines.

To make optimal use of the small part size and the need to make a large number of parts, a shuttle type machine was desired. A machine that could make between 6 – 8 parts per mold per cycle was deemed reasonable. A machine from Bekum America Corporation, H-111, was selected as the optimal machine. The machine has six extruder heads, giving it the capacity to extrude enough material for 6 parts to be made per mold, as well as the ability to shuttle between two molds rapidly. This particular model is the smallest double station continuous extrusion model available. Any larger would be unnecessary and expensive.

Since this project is utilizing insert molding, additional parts will need to be added to the selected machine in order to facilitate placement of the inserts into each cavity. Optimally, a simple attachment to each mold’s blow pin rack would place the inserts just prior to the blow pin rack descending to blow the parts.

A continuous extrusion type head was selected for this project. The BKZ Head from Bekum was selected. It can extrude 6 parisons at a time, and is recommended by Bekum for Polycarbonate. The small part size is what allows the material to be continuously extruded. Continuous extrusion in combination with two mold shuttle type machine will significantly reduce cycle time. Maintaining the tight tolerances of a rifle cartridge is the primary influence on head selection. The primary concern is that the overall part dimensions adhere to the U.S. Army standards. Another major concern is the cost of the part, machine, and mold. Using a continuous extrusion machine significantly reduces the overall machine cost. While wall thickness variation is acceptable, so long as the part is no thinner than 1mm at the tip and the overall dimensions remain consistent, it is not a major concern. The small part volume accommodates rapid extrusion, so the chance of the PC/ABS blend degrading is reduced, which is crucial in ensuring the part maintains tolerances. Avoiding degradation is also crucial in minimizing the potential for surface defects, which would prevent the part from performing properly.

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DESIGN DRAWINGS

Figure 28 – Isometric Views of Blank Cartridge

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Figure 29 – Blank Cartridge Dimensions

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Figure 30 – Blank Cartridge Dimensions (Angles)

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Figure 31 – Blank Cartridge Section View

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Figure 32 – Blank Cartridge Mold

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Figure 33 – Blank Cartridge Mold – Water Line Location

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References:

A Guide to Plastics Commonly Used in Blow Molding http://www.custom-pak.com/news/guide-plastics-commonly-used-blow-molding/ (accessed Feb 2, 2018)

5.56mm (5.56 x 45 mm) Ammunition Gary's U.S. Infantry Weapons Reference Guide http://www.inetres.com/gp/military/infantry/rifle/556mm_ammo.html (accessed Feb 2, 2018).

A (Very) Short Course in Internal Ballistics http://www.frfrogspad.com/intballi.htm (accessed Feb 2, 2018).

Ammunition handbook; Headquarters, Dept. of the Army: Washington, D.C., 1981.

Barnes, F. C.; Woodard, W. T. Cartridges of the world: a complete and illustrated reference for more than 1500 cartridges; Krause Publications: Place of publication not identified, 2016.

Cutshaw, C. Q. Tactical small arms of the 21st century; Gun Digest Books: Iola, WI, 2006.

Leibenluft, J. How do you safely drop supplies and ammunition from the air? http://www.slate.com/articles/news_and_politics/explainer/2008/04/dropping_bullets_from_a_plane.html (accessed Feb 2, 2018).

Pike, J. Military https://www.globalsecurity.org/military/systems/aircraft/systems/500-lvad.htm (accessed Feb 2, 2018).

U.S. Military Ammunition http://olive-drab.com/od_firearms_ammo_us.php (accessed Feb 2, 2018).

Understanding Pressure https://www.primalrights.com/library/articles/understanding-pressure (accessed Feb 2, 2018).

“5.56mm (5.56 x 45 mm) Ammunition Gary's U.S. Infantry Weapons Reference Guide.” 5.56mm (5.56 x 45 mm) Ammunition, www.inetres.com/gp/military/infantry/rifle/556mm_ammo.html. Accessed 2 Feb. 2018.

Advanced Elastomer Systems. Extrusion Blow Molding Guide for Thermoplastic Rubbers and Thermoplastic Elastomers; 2001.

Chevron Phillips Chemical Company. Die Shaping for Extrusion Blow Molding. 2002, No. TSM-13, 1–6.

Kazmer, D. O. Injection mold design engineering; Hanser Publications: Munich, 2016.

Extrusion Heads http://bekumamerica.com/extrusion-heads/ (accessed Feb 9, 2018).

H-Series http://bekumamerica.com/h-series/ (accessed Feb 9, 2018).

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Appendix

Attachment 1:

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Attachment 2:

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Attachment 3:

Mathcad Calculations:

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Attachment 4:

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