Mold Validation Procedure Part-1

Yes Mold validation is very Important to avoid any Future Quality & production Related problem, But as actual we always Noticed that due to short period of time you can say customer want mold As early as possible, There always many parameter you will face problem so Question is that Is all the molds need to be verified I will say Yes, There is Many scientific way to validate the Injection, Blow molds Simple way to analysis the process parameter which is required to get the desired Quality. perform the MCA (Multicavity analysis) PCA (Process capability Analysis)activity to validate any molds

OK Lets Go Through procedure:
Scope/Purpose:
1.1 The purpose of the Validation Procedure for Blow Molds is to identify a capable mold and process that will achieve key part dimensions, attributes and weight. It is also the purpose of the Validation Procedure for Blow Molds to establish a processing-window for the blow molds. This document provides a detailed description of the steps that will deliver the types of results a qualification process is designed for.

It should be recognized that training in design of experiments and statistics, e.g., interpretation of control charts, is needed and that terminology in the blow molding industry varies throughout different regions of the world. Please make use of the glossary at the end of the document to better define terms. Examples are provided for each step of the mold qualification process to assist in understanding the procedure and qualifying the mold.

1.2 The extrusion blow molding cycle is broken up into the following segments:

Parison Extrusion -> Mold Close -> Parison Blow -> Cool -> Mold Open -> Part Ejection

The blow molding process is a complex process that is controlled by four categories of processing variables: Temperature, Flow Rate, Cooling Rate, and Pressure.

Temperature Flow Rate Cooling Rate Pressure
Melt Temperature Extrusion Rate Mold Temp Blow Pressure
Coolant Temperature Coolant Water Rate Coolant Temp Melt Pressure

Some combination of settings for these process variables will provide an optimum molding process capable of producing molded containers to within container specifications. In addition, the molds will have a window of process variable settings that will provide parts within specification.

The objective of the Validation Procedure for Blow Molds is to determine molding process conditions that provide production personnel maximized process capability and process adjustment range while maintaining a capable, controlled process. Applying statistical methods to evaluate the molds and the process should help identify key process variables for evaluation. The Validation Procedure for Blow Molds will also serve as a standard for process optimization so that terms, specific procedures and result data formats are defined. The document may be used as a reference resource after the methods have been successfully implemented. One of the goals of the Validation Procedure for Blow Molds is to develop a common platform for mold and process evaluation and to maintain efficient communication practices.

Procedures

The following steps are required in validating a blow mold with the overall process shown in figure 1:
4.1 Mold Certification (page 7)
4.2 Mechanical Mold, Head Tooling and In-Mold Labeling Debug (page 10)
4.3 Design of Experiments (page 31)
4.4 Qualification (Process Capability Study) (page 48)
4.5 Mold/Neck/Push-up Steel Adjustments (Process Centering) (page 62)
4.6 Verification (30 Day Run) (page 64)

5.0 Attachments
5.1 Table of Constants and Formulae for Control Charts (page 65)
5.2 Control Chart Interpretation: Three Basic Rules -> C, P, R (page 66)
5.3 Histogram Construction (page 67)
5.4 Capability Analysis Cookbook (page 68)
5.5 Standard Normal Distribution Table (page 69)
5.6 Product Quality Measures (page 70)
5.7 Example of DOX worksheet for process conditions and variables (page 71)
5.8 Safety Precautions For Blow Molding (page 72)
5.9 Glossary of Blow Molding Terms (page 73)


Blow Mold Validation Flow Chart

Flow Chart

Figure-1



Figure-2


Figure-3

Mold Certification

The purpose of Mold Certification step is to verify cavity and mold base dimensions and materials of mold construction. Cavity and neck insert dimensions, mold cooling channel diameter dimensions, cooling line connector diameter dimensions, mold backing plate mounting hole pattern, mounting bolt hole diameter dimension and mounting bolt hole thread type should be verified with the mold and blow molding machine platen prints. Dimensions for the mold mounting bolt holes and the bolt hole pattern in the mold backing plates are verified to help avoid machine scheduling delays during mold installation, initial start-up and process optimization procedures.

The Mold Certification procedure should be performed at the mold builder to expedite any required mold modifications and to help avoid delays during mold installation, process start-up and process optimization procedures. Mold Certification documentation must be provided by the mold builder for review before the molds are shipped to the production blow molding plant.

Use of the specified materials in mold construction help to ensure the required level of mold mechanical integrity necessary to meet production run requirements. The specified materials of mold construction also provide the required level of heat transfer characteristics in the neck insert, cavity and pinch-off areas during production.

Mold cooling channel and cooling line connector dimensions should be verified so that heat transfer in the mold is optimized and so that cooling control may be maintained during production.

Cavity and neck insert dimensions should be verified to establish the mold dimension ‘base line’ before process optimization procedures are initiated. The ‘base line’ dimension data may be used later in the process optimization procedures and for process centering purposes. Table 1 may be used to tabulate the mold certification data. Refer to figure 3 for neck finish nomenclature and dimensions.

Table 1: Mold Certification Data








4.2 Mechanical Mold, Head Tooling and In-Mold Labeling Debug

The purpose of the Mechanical Mold, Head Tooling and In-Mold Labeling Debug is to test the mechanical operation of the mold, mechanical and electrical operation of the extrusion die head and the mechanical and electrical operation of the in-mold labeling mechanism to reveal any gross design, construction or operational problems.

The Mechanical Mold Debug should be performed at the tool builder to ‘dry cycle’ the mold. Inspect the mold(s) and verify leader pin and bushing alignment, mold shut height, cavity parting line match, ejection system component function and expedite any required mold adjustment evident from the debug. If completed off site, a tool builder representative must be present to make necessary adjustments as required. The mold must run without flash and must meet cosmetic quality requirements, e.g., no drag lines or poor surface finish, no parting line mismatch, etc. Upon request, the tool builder should be able to provide verification of all critical steel tolerances and that these were made "Steel Safe".

The Head Tooling Debug should be performed at the plant site on the production blow molding machine. The operation of the moveable, mandrel or the die should be tested for full range motion at operating temperature. Movement and position of the mandrel or die should be calibrated with the parison program controller and verified for repeatability. A specified, operational tolerance ‘fit’ between the mandrel outside diameter and the guide bushing inside diameter should be verified. If excessive wear is evident, the mandrel and/or guide bushing should be replaced before the process optimization procedure is initiated. The melt flow surfaces on the mandrel should be inspected for any physical damage or excessive wear and repaired or replaced as required.

Range of centering adjustment for the die (bushing) and the die adjustment bolts should be verified for operation. The die and adjustment bolts should be free of any degraded material and must be adjustable at normal operating temperatures. The melt flow surfaces on the die should be inspected for any physical damage or excessive wear and repaired or replaced as required.

When die ovalization is required, verify that the melt flow surface contour dimensions agree with the die design print. Ensure that the die is installed in the proper position (orientation) relative to the mold parting line. Scribe a reference line on the outside surface of the die so that the die(s) may be assembled in the proper position after cleaning or repairs.

The In-Mold Labeling Debug should be performed at the plant site on the production blow molding system. IML (In-Mold Labeling) system designs are developed specifically for shuttle or wheel blow molding machines and require different set-up and operation procedures, respectively.

IML system components are adjustable and can support a range of label, mold cavity and container design configurations. Primary components in the IML system for the shuttle blow molding process include the following:

• Placer Arm Assembly - Consists of the vacuum cup heads and the mechanism to operate them to pick labels from the magazines and places them into the mold cavities.

• Tow Bar Assembly - Connects to the inserter to the mold platens and defines the position of the Placer Arm Assembly relative to the mold cavities and maintains that position.

• Magazine Adjustment Assembly - Holds the label magazines and allows them to be repositioned to change the label location on the container.

IML systems for shuttle blow molding machines have 3 basic areas that require adjustment for label positioning:

• Inserter Position Relative to the Mold Cavities
• Magazine Adjustments
• Label Pick Program

Label positioning can be optimized with trial adjustments. Section 4.2.5 IML Setup provides system adjustment procedures for label positioning with the shuttle process.

The following steps are part of the Mechanical Mold, Head Tooling and In-Mold Labeling Debug:

Step 4.2.1: Select Head Tooling

Step 4.2.2: Parison Centering

Step 4.2.3: Manifold Balance

Step 4.2.4: Verify Process Operation

Step 4.2.5: IML Setup
Mechanical Mold, Head Tooling and In-Mold Labeling Debug
Step 4.2.1: Select Head Tooling

Purpose:

The purpose of the Select Head Tooling step is to provide a guide for determining the correct mandrel and die bushing size for the blow molding machine head tooling assembly. Mandrel and die dimensions are estimated based on container dimensional data, container symmetry, blow-up ratio, targeted container weight, neck finish requirements and the type of material (degree of parison swell) that will be used to produce the container.

An initial blow-up ratio must be calculated using the container design dimensions and the required parison diameter.
The required parison diameter will depend on the relative size of the container, the container design (handle or no handle) and the container neck finish requirements. Initial blow-up ratios may be calculated using the following equation.

Blow up ratio = Bd / Nd

where: Bd = Bottle diameter, in
Nd = Minimum neck diameter, in

The blow-up ratio is compared with the maximum recommended blow-up ratio of the selected material.
Figure 2 shows a typical blow molded container with dimension and design nomenclature for reference.

Blow up ratios of 2 or 3 to 1 are considered normal when molding commodity resins such as polyethylene. A blow-up ratio as high as 4:1 is a practical upper limit. The blow up ratio for large containers with a small neck, is generally extended to 7:1 so that the parison fits within the neck and so that there is no mold parting line mark on the neck finish. Blow up ratios for a containers with a handles are generally in the 3 or 5 to 1 range as the die diameter must be larger to allow the handle to be blown.

In order to properly estimate and ‘size’ mandrel and die geometry for the blow mold(s), and to effectively control the process, a thorough understanding of parison swell and draw down phenomena is required. Parison swell is a combination of diameter swell and weight swell. It is a difficult blow molding property to estimate and to control. The parison diameter swell is a complex function of the weight swell, the rate of swell, and the melt strength.

Parison swell behavior varies significantly depending on material type, material processing conditions, machine processing parameters, basic die design (diverging vs. converging), container geometry (required parison diameter), container weight (shuttle process) and type of blow molding process. Some of the wheel type blow molding processes clamp (pinch off) and hold the parison at both ends during the blowing sequence in the process. The parison swell effects are normally more readily controlled on the wheel process compared with the shuttle process.

Parison swell data for a given material is often not available for mandrel and die calculations. The alternative is to proceed in a stepwise approximation towards the desired mandrel and die dimensions, and through trial and error, towards the targeted container weight with the aid of an interchangeable set of dies.

Internal die design dimensions including approach angles and land lengths vary significantly with blow molding machine capabilities and machinery manufacturers experience. Calculations for these dimensions are beyond the scope of this document and will not be discussed here.

However, as a rule of thumb, when blow molding commodity materials (PE, PP), a die land length of at least 8 times the annulus gap (die gap) is typical.
Blow Molded Bottle Nomenclature



A simplified approach for calculating and estimating mandrel and die dimensions is presented here to serve as a general guide. The following equations may be applied in cases where the container geometry is symmetrical and there is no handle on the container.

Case A

When the neck size of a container or the smallest diameter of the container is the controlling feature (as when the parison must be contained within the smallest diameter) , the following approximations may be used to calculate the dimensions of the mandrel and die. Use of these equations assume a free-falling parison and they can be used with most PE blow molding materials.

Dd = 0.5 N d (Equation 1.1)

Pd = ( D d2 - 2Bdt + 2t2)1/2 (Equation 1.2)

where: Dd = Diameter of die bushing, in
Nd = Minimum neck diameter, in
Pd = Mandrel diameter, in
Bd = Bottle diameter, in
t = Bottle thickness at Bd, in

Case B

When the container weight is specified instead of the wall thickness for a process using inside-the-neck blowing, the following equations may be applied:

(The equation may be applied for a free-falling parison, and is applicable to most irregularly shaped containers.)

Pd = (Dd 2 - 2 (W/T2) Ld)1/2 (Equation 1.3)

where: Pd = Mandrel diameter, in
Dd = Diameter of die bushing, in
W = Weight of container, g
L = Length of container, in
d = Density of material, g/cc
T = Wall thickness, in

Case C

When a parison is partially controlled by tension, i.e., the rotary wheel blow molding process, the following relationships may be used. The assumption here is that the parison is not free-falling.

Dd * 0.9 N d (Equation 1.4)

Pd * ( Dd 2 - 3.6 Bd t + 3.6 t 2)1/2 (Equation 1.5)

Pd * ( Dd 2 - 3.6 ( W / T 2 ) Ld) 1 / 2 (Equation 1.6)


where: Pd = Mandrel diameter, in
Nd = Minimum neck diameter, in
Dd = Diameter of die bushing, in
W = Weight of container, g
L = Length of container, in
d = Density of material, g/cc
T = Wall thickness, in
Bd = Bottle diameter, in
t = Bottle thickness at Bd, in

Case D

Estimating head tooling dimensions for containers with handles requires an empirical method based on container size and geometry. When the container has a molded handle use the following equations to determine the estimated dimensions for the head tooling die and mandrel.

The die diameter can be estimated using equation 1.7 and the container dimension data.

D = ( 0.8 Z ) / 3 Equation 1.7

Where: Z = Maximum container width or diameter
D = Diameter of die bushing, in.

The die diameter, D, is then substituted in equation 1.3, equation 1.5 or equation 1.6 depending on available container data and the blow molding process that will be used.


All the steps during the procedure that involve intimate contact with the blow molding machine are to be done by a qualified blow molding machine operator.

Procedure:


Mechanical Mold, Head Tooling and In-Mold Labeling Debug
Step 4.2.2: Parison Centering
Purpose:

The purpose of the Parison Centering step is to establish a preliminary die position adjustment to achieve stable parison extrusion and uniform, circumferential parison wall thickness distribution. The ‘fine’ adjustments of the die will be completed later in the Container Performance Optimization step 4.3.2 (page 35) of this document.

Die bolts should be free of any degraded material and turn freely over the adjustment range at normal operating temperature for the die bushing. Appropriate repairs should be made for damaged threads on either the die bolt(s) or the die bushing.

Procedure outlines for the shuttle and wheel blow molding processes follow, respectively:

Shuttle Process Procedure:




Wheel Process Procedure:






Mechanical Mold, Head Tooling and In-Mold Labeling Debug
Step 4.2.3: Manifold Balance

Purpose:

The purpose of the Manifold Balance step is to evaluate the thermal and melt flow balance of the head tooling manifold distribution system and to establish uniform melt flow to each die on multi-head blow molding systems. The melt flow control (normally a choker valve) must adjust freely at normal operating temperature. The valve design must be capable of adjusting material flow to each die head so that the melt flow is stable over a range of extrusion rates.

Both the parison weight and length differences are an indicator of the degree of melt balance control and the quality of the manifold system design. A typical, well balanced manifold will be balanced to within 5%. It is critical to have the flows balanced to each die or the part-to-part variation may be large and process capability may not be achievable.

Initial manifold control valve balance adjustments should be made during the Parison Centering step to optimize the manifold system flow balance. The Manifold Balance step may have to be repeated at higher extrusion rates, i.e. production rate, as melt flow pressure gradients change with melt flow rate and can affect the manifold melt flow balance.

Proceed to the Verify Mold Operation step if the blow molding machine is a single die head system.

All the steps during the procedure that involve intimate contact with the bow molding machine are to be done by a qualified blow molding machine operator.

Shuttle Process Procedure:






Figure 4 depicts typical results for a manifold which is not properly balanced, i.e., parison 9, 10, and 12 are not within 5% of the weight of the control parison #7. Further balance adjustments must be made in order to bring the manifold system into balance.
Table 2: Manifold Balance Test Results





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