Reducing defects in producing expendable mold with 3D printers in NCSU rapid prototyping lab

Team : Wolf Improve

Members:

VIGNESHWAR MANOKARAN

ASHWATH PARTHASARATHY

Agenda

• Project Charter

• SIPOCDefine

• KPI

• Run Chart

• MSAMeasure

• Brainstorming

• C&E diagram

• Screening Design

• ANOVA

Analyze

• Response surface analysis

• Confirmation RunImprove

• Modification of Standard Operating ProcedureControl

2

DEFINE PHASE

PROJECT CHARTER

Problem Statement

Executive Sponsor: ISE Projects Lab

The current FDM machines in the ISE projects lab produces 40% (4 out of 10 defective) of parts out of the specified limits, which has total dimensional deviation of more than 0.05 inch

Champion: Dr. Timothy Clapp

Mission Statement and Scope Reduce the number of defective parts to 10% (1 out of 10) by April 29, 2013.

Team Members Ashwath Parthasarathy Vigneshwar Manokaran

Scope In scope: 3D printer process parameters and design /Out of scope: Print files, Printer material. Key Stakeholders:

ISE Project lab. Harshad Srinivasan (Lab in-charge) Dr. Jason Low

DMAIC Plan Start Plan End Operational Metric(s) Baseline Target

Define Jan 20 Feb 20 Quality level: % defective Total Dimensional Deviation (inch)

40% 10%

Measure Feb 22 Mar 12

Analyze Mar 15 Apr 12 Defect Definition: Component whose sum of deviations in x, y and z axis exceeds 0.05 inch is considered defective

Expected Benefits Projected Savings (US$)

Improve Apr 13 Apr 20 Hard Benefits:, Reduced rework cost, Better accuracy of finished parts

$ 2500

Soft Benefits: Improved production, Reduced scrap, Customer satisfaction and reduced material usage.

Control Apr 21 Apr 29 Strategic/Other Qualitative Benefits: More students use 3D printing for rapid-prototyping parts.

semester

DEFINE PHASE

PROCESS MAP - SIPOC

Project: 3D printing of wolf model

Team: Ashwath Parthasarathy, Vigneshwaran Manokaran

Date Revised: 2/20/2013

SUPPLIER INPUT PROCESS OUTPUT CUSTOMER

NC STATE Student CAD file of the model CAD file to STL STL File Slicing software

Computer Aided

Design DocumentSTL file STL File to Slicing Build File G Code, M code

G-code, M-code file

Code file, Part

material, support

material

Part material, support

material

Fused deposition

method prototypingNC State Student

MEASURE PHASE

KEY PERFORMANCE INDICATORS

KEY PERFORMANCE INDICATOR MEASUREMENT TOOL

THICKNESS(BOTTOM) inches SCREW GAUGE

THICKNESS(TOP) inches SCREW GAUGE

LENGTH (inches) VERNIER CALIPER

BREADTH (inches) VERNIER CALIPER

Response variable: Total Deviation (inches)

Total Deviation= (Thickness(top)- actual )+(Thickness(bottom)-actual)+

(Length-actual)+(Breadth-actual)

MEASURE PHASE

RUN CHART- DEVIATION

Upper Specification Limit: 0.0525

Sample size: 6

Number of defects: 2

% defects : 33.33%

MEASURE PHASE

MEASUREMENT SYSTEM ANALYSIS

Component % contribution of Total

Gauge R&R 2.37

Repeatability 2.37

Part-to-Part 97.63

• Measuring Tool - Vernier caliper & Screw gauge• No. of operators - 1, hence error due to

reproducibility.• Type of parts - 2

Result:• The variation due to Gauge is less than

10%, hence the measurement system can be used without any modification.

ANALYZE PHASE

ROOT CAUSE ANALYSIS – RESULT OF BRAINSTORMING

Motor-High inertial

mass affecting tool

motion

Table- not horizontally

held by the point

contact

Material-exposed to

environmental which

affects its properties

Base-No vibration

separator between

base table and the

machine

ANALYZE PHASE

ROOT CAUSE ANALYSIS – CAUSE AND EFFECT DIAGRAM

DIMENSIONAL

VARIATION

ANALYZE PHASE

ROOT CAUSE ANALYSIS – 5 WHYS

Defective Components produced

Tool head not under precise control

High inertial mass on tool head

Improper speed and pattern of

printing

Inappropriate setting of process

parameters

Machine tolerance out of specification

ROOT CAUSE

WHY

WHY

WHY

WHY

WHY

ANALYZE PHASE

ROOT CAUSE ANALYSIS – PROCESS PARAMETERS

The process parameters that could affect the final dimension are

identified from the previous analysis as:

PARAMETERS TYPE LEVEL/RANGE

LAYER THICKNESS (inch) CATEGORICAL 0.125, 0.25, 0.5

SPEED MULTIPLIER CONTINUOUS 0.5x-1.3x

FLOW RATE (RPM) CONTINUOUS 6-60

FILL DENSITY (%) CONTINUOUS 10-90

A screening design was created to identify the parameters that have

a significant effect on the final dimensional accuracy. Dimensional

deviation is taken as the response variable.

ANALYZE PHASE

ROOT CAUSE ANALYSIS – SCREENING DESIGN

• A half factor factorial design with 8 runs was conducted for screening.

Half fractional factorial experiment data table

Figure shows 5 different samples

ANALYZE PHASE

ROOT CAUSE ANALYSIS – SCREENING DESIGN RESULTS

PARETO CHART:

• From the analysis, it is found that the interaction effect between Flow rate and Fill density and the effect of Layer thickness are significant.

• A model is created with main effect of Flow rate, Fill density, Layer thickness and interaction effect of Flow rate and Fill density.

• The main effect of Fill density and Flow rate are included in the model as their interaction effect is significant.

QUANTILE PLOT:

ANALYZE PHASE

ROOT CAUSE ANALYSIS – FINAL MODEL

• After removing the insignificant terms the following model was

obtained, it will be used as the model for further full factorial

analysis.

TOTAL DEVIATION = 0.0408125 - 0.005688(LAYER THICKNESS) + 0.0011875(FILL DENSITY) + 0.0024375(FLOW RATE) + 0.0063125(FILL DENSITY * FLOW RATE)

ANALYZE PHASE

ROOT CAUSE ANALYSIS – ANOVA TABLE

• R2 adjusted is 0.88, hence the model explains most of the

variations in the data.

• As the ANOVA table indicates, the model effect is significant.

Source DF Sum of Squares Mean Square F Ratio

Model 4 0.00063638 0.000159 15.1068

Error 3 0.00003159 0.000011 Prob > F

C. Total 7 0.00066797 0.0250*

IMPROVE PHASE

RESPONSE SURFACE ANALYSIS-CENTRAL COMPOSITE DESIGN

• A central composite design was constructed for layer

thickness of 0.125 mm (most commonly used layer thickness).

• A response surface was created and the optimal process

parameters were identified.

From the RSA it was found that the optimal values are

Fill Density = 10 %

Flow rate = 49.673 RPM

CONTROL PHASE

MODIFICATION OF THE STANDARD OPERATING PROCEDURE

• The SOP which is the lab manual given to all the users of the

lab has to be updated with the latest findings.

Excerpt from SOP before change

Area to be

updated

Q?18