Seminar Report

Medical Plastics : Materials, Applications And Processing

For Medical Devices And Pharmaceuticals Industries

EFFECTIVE MOULD MAKING

Planning & Coordination for Medical Components

Flow Chart

Constructing Medical Injection Molds

Part Design Planning

                                                                           -Design for optimum performance

Selecting of Mold Maker

                                                                      -Audit of Potential Candidates

Hot Runner Design/System

                                                                            - Meetings with Hot Runner Suppliers

Computer Simulated Analysis

                               - Mold Flow

                               - Mold Cool

                                                   - Finite Element Analysis

Prototype Mold Design

                                                                       - Simulate Plans for Production Mold

Single Cavity Tool Construction

  - Progress Update

  - Discussions on Product Function

Evaluation of Single Cavity Mold & Parts

                                                                                 - Plan Production Mold Action,

                                                                               Runner System, Stack Up

                                No

Proceed to

Production

Mold

                                  Yes

Production Mold Design Process

                                                     - Mold Size

                                                            - Steel Selection

                                                                  - Tolerance Analysis

                                                            - Mold Coatings

Production Mold Construction

                                                                 - Progress Updates

                                                                                       - Discussions on Product Function

Evaluation of Mold & Process

Mold Validation Process

MOULD MAKING STEPS

Traditional Approach

• Manual Free Hand Sketching
• Shapes, Size and Ideas Crystallised
• Preparation of 2D Drawing with detailed Dimensions
• Preparation of 3D Model From Wood, Paper, Plaster of Paris, Epoxy, Clay etc.
• 2D Engineering Drawing free zed
• Pattern Making for Casting / Copy Milling Aid.
• Mould Manufacturing by conventional methods
• Mould Trial on simple Injection Machines

Advance CAD-CAM Approach

• Use of Auto -CAD to prepare 2D and 3D Drawing of a product
• Rapid Prototyping for model making and Rapid Tooling
• Mould Design by CAD and Analysis by high End solution Software
• Mould Manufacturing by CAM
• Mould proving on micro Processor based

Certain aspects of mould design cannot be discretely separated from part design. Gating is one. The size and the location of a gate (or gates) and the design of the melt-flow path can substantially influence part performance.

Small gates not only cause incomplete filling or packing of the cavity, cold Flow marks, and jetting, but also produce weak weld lines. Good weld line strength is achieved by a hot flow front. Fast fill rates needed to maintain a hot flow front can cause excessive blush around a small gate. Incomplete cavity parking prompts higher injection and hold pressures during moulding, which in turn cause higher stresses in the gate area. Many a crack has been found, during failure analysis, to originate from highly stressed gate areas.

The use of mould-filling analysis has made the design of proper flow paths in the mould cavity quite easy. Gate location for better weld line strength and weld line placement with single or multiple gates is no longer a matter of trial and error. The analysis, generally performed during the final stages of part design, also provides feedback on appropriate wall thickness for mould ability. This protects against the mistake of designing a thin wall that may be strong enough structurally but not thick enough for moulding without the use of higher injection pressures, which may cause high stresses.

Weld lines are areas of weakness in parts. Hence, they should be placed away from the regions that may be subjected to service stresses. The part of a snap-fit assembly that could not withstand deflection and cracked during assembly at the weld line. A quick redesign, with minimum tool modification, that eliminated the weld line without sacrificing functionality.