Take into account the ablationd the design part.
Definitions:
? Tolerances -Are Given by Designer to Designed Dimensions
? Deviation and Ranges – Are the Results of Production
? Range -The Differente Between The Smallest and the Larget Measurement of a Dimension in a Batch of Produced Paster
Product Dimensions by Analyzing The Shrinkage.
The follow analysis is limited to:
? Dimension Shrinkage only (not for distortion)
? No Change in inject Parameters
Simple Example
For Illustration Purposes, Let us start with a simple exmple (all directnsions in mm). SEE FIGURE 1:
FIGURE 1: Sketch of a Simple Part.
: In Order to Meet the Nominal Dimension (2.0) The Cavity Dimension Will Be 2.0408mm. In the Same Part We Have Another Diminsion= 204.08 mm. SEE FIGURE 2.
FIGURE 2: Mold Dimension to Receive Nominal PART DIMENSION.
Dimensions of the Cavity in the MOLD are fixed so shrinkage will be calculated from thedisensions.
On our simple part, Each Dimension Can Reach the Tolerance Limits. Now we can check what the shrinkage should be for eACH DIMENSION in order to reader limits. See Figure 3.
Figure 3: Shrinkage of the part that is needed to reach the tolerance limit.
Analysis of shrinkage to tolerance limits:
1. Dimension 1-2.0 ± 0.1mm
a. Shrinkage from Mold Size to Maximum is imageible.
b. SHRINKAGE from MOLD SIZE to Minimumum Dimension is Also IMPOSSIBLE. It ’
c. Differente Between Minimum and Maximum Tolerance is 10% From Dimension.
D. This Means that there is almost no change that this dimension will be out of tolerance.
2. DIMENSION 2-120.0 ± 0.1mm
a. The Shrinkage FROM MOLD SIZE to the Maximum Allow Dimension is 1.95%.
B.
c. Differente Between Maximum and Minimum Tolerance is 0.1% from Dimension.
D. This Means that it will be much more different to product this directnsion with tolerance.
e. When the average shrinkage is not elm to 2% it will be almost impossible to problem
% From Dimension, The Range of Shrinkages of Dimension 2.0 ± 0.1mm Will Also Be 0.1% (0.002mm). SEE FIGURE 4.
Figure 4: Calculation of Shrinkage Results where is equal for both Dimensions.
Then, then
Calcuration of Percentage of Tolerance from Drawing Dimension (POT) IS:
Where:
T – Tolerance
D -Dimension
POT -Percentage of Tolerance from Dimension
The port is defined by the part designer.
How do we know what the port is that can be app it? We have to connect it to the product capability.
Calculation of Percentage of Range from Average (POR) is:
The Production Capability Can Be Measud with The Percentage of the Range from Average (POR).
CALCULATION of POR:
Where:
R – Range of Results
A -AVERAGE of Results
POR -PERCENTAGE of Range from Average
POR is a Result of Production
? Selection of the Right Por Should Be Based on Data Collection from Production
? POR Depends on the Quality of the Inject Process
? The more account the process, the lower the por. For exmple:
3 raw material.
3 More Accurate Machines
3 More Accurate Molds with Efficient and Uniform Cooling
3 Stable And Repeature Injection Process with Big Injection Window
3 USING MATERIALS with Low Shrinkage
3 Uniform Climate of Injection Molding Facility (Air-CONDITITINED)
3 and so on
- to begin the process, we can take a general exten number to all directnsions
- GOOD Start for Por Can Be 0.2% to 0.3%
- Later on, after data collection, this number can be updated
Now we can connect the extens.
Real Drawing Analysis (Based on a Real Part Drawing – Not Shown Here)
We used excel for this analysis (Figure 5):
Columns 1, 2, 3 and 4 will be filled with the dimension no. Along with the specifyness and tolerances from the drawing.
In colorn 5, the pot will be?
The Expected Por (Percentage of Range from Average) is Shown in Column 6. It is 0.2% for a starting point.
Now we rink the diarsions account to column 5 (POT) from Smallest to largest.
FIGURE 5: Drawing Dimensions, Tolerances, POT and POR.
Now we product a graph from data that will show the analysis of the drawing and tolerances with related.
FIGURE 6: Analysis of Drawing Dimensions. Expected Range of Each Dimension with Relation to the TOLARANCE BORDERS, TAKING Into Account the General Por During Production.
All dimensions in this graph are normalized to percentage. The upper and lower lines represses the maximum and minimum limits, 50% above the nominal and nominal and nominal and nominal and normal.
The Vertical Red Lines Repressent The Distancen The Expected Ranges For Each Dimension with Relations Limits.
The lower the port, the more different it will be to propuce the part (and vice-versa).
The Higher The Por the more different it will be to produce the part (and vice-versa).
Analysis of Measurement Results
Now we add the measurement results. See Figure 7.
FIGURE 7: Measurement Results and Calculation of Average, Maximum and Minimum to Each Dimension.
Columbus 1 to 27 Show Measurement Results (there is no limit to the number of meetments). At the end, then, is a call, Maximum and Minimum for Each Dimension.
From this data, we product a graph with all the results. See Figure 8.
FIGURE 8: Results of Actual Measured Data, Average, MIN and Max to Each Dimension and the Expected Por.
Now Results can be analyzed:
? The Blue Line is the Minimum MEASURED for Each Dimension
? The YELLOW LINE is the Average Calculated for Each Dimension
? The Dark Purple is the Maximum MEASURED for Each Dimension
is more than 2%.
? The Expected Por (Vertical Red Line) is around the average of each measured design.
? Measurements ABove Zero Shrink Are Less than Anticipated (and are theReface Larger).
? Measurements Below Zero Shrink are more than anticipated (and are theReface Smaller).
? Measurements 1 and 2: The actual range is much Lower than exten (vertical red line is much Longer than the difference between the dark purple line and the block line).
? MeaSurement 5, 8 and 7: The actual range metapctation.
minimum and the maximum.
Conclusions:
After collecting enough data, The Prediction of Por Will Be Much More Accurate. The data can be collected with related to: Materials, Type of Molds, Size of Molds, MACHINES ETC.
This suggest itver enables us to:
? Analyze the featureded the Customer ’s PART SPECIFICION BEAFORE EHE ENTMESTMENT and Communication Stages
?
? Determine the posSIbility of Finding Measurement Error.
This method can wait the footowing:
? For the Designer of Plastic Parts
? Define Tolerances to Dimension -Feasibility of Meeting The Customer ’s Requirements/Specifications.
? The Sub-Contractor of Inject Molded Parts Before Accepting Order for New Product.
? Checking the Possibility to Meet Drawing Requirements and To Select Critical Dimensions
? MOLD MAKER
? Checking the Possibility of Meeting Customer Requirements
? MOLD TEST T1
? Checking All Drawing Dimensions
? Analysis of Crital Dimensions and Ability to Produce The Parts
? Quality Control
? To Give Focus on Critical Dimensions that are injecting parts discicult injection molded parts to print
? To Find Measurement Mistakes