injection molding

Design for Manufacturing (DFM) and design for assembly (DFA) are the integration of product design and process planning into one common activity – injection molding.  The aim is to design a product that is easily and economically manufactured. The importance of designing for manufacturing is underlined by the fact that about 70% of manufacturing costs of a product (cost of materials, processing, and assembly) are determined by design decisions, with production decisions responsible for only 20%. The heart of any system is a group of principles or guidelines that are structured to help the designer reduce the cost and difficulty of manufacturing an item.

Concepts for Good manufacturing design

1. Reduce the number of parts. 

This is probably the best opportunity for reducing manufacturing costs.  Fewer parts means fewer purchases, processing & development time, equipment, assembly issues, quality inspection and testing. It reduces the level of all activities related to the product during its life.  A part that does not need to have relative motion with respect to other parts, does not have to be made of a different material, or would makes the assembly or service of other parts extremely difficult, makes the part a target for elimination.

One approach to part reduction is based on the use of one-piece structures and selection of manufacturing processes such as injection molding, extrusion or precision castings.

2. Avoid separate fasteners. 

The use of fasteners increases the cost of manufacturing a part due to the handling and feeding operations that have to be performed. Besides the high cost of the equipment required for them, these operations are not 100% successful, so they contribute to reducing the overall manufacturing efficiency.

Generally speaking fasteners should be avoided and replaced, for example, by using tabs or snap fit clips. If fasteners have to be used, then some guides should be followed for selecting them. Minimize the number, size, and variation used; also, use standard components whenever possible. Avoid screws that are too long, or too short, separate washers, tapped holes, and round heads and flatheads. Self-tapping and chamfered screws are preferred because they improve placement success.

3. Use of standard components. 

Standard components are less expensive than custom-made items. The availability of these components reduces product lead times.  Also, their reliability factors are well established.  The use of standard components refers to the production pressure to the supplier, relieving in part the manufacture’s concern of meeting production schedules.

4. Design for ease of assembly. 

Select the optimum combination between the material and assembly process to minimize the overall manufacturing cost. In general, final operations such as painting, polishing, finish machining, etc. should be avoided. Excessive tolerance, surface-finish requirement, and so on are common problems that result in higher than necessary production cost.

5. Product Handling. 

Consists of positioning, orienting, and fixing a part or component. To aide orientation, symmetrical parts should be used when possible. If it is not possible, then the asymmetry must be exaggerated to avoid failures. Use external guiding features to help the orientation of a part. The subsequent operations should be designed so that the orientation of the part is maintained.  Avoid using flexible parts – use slave circuit boards instead. If cables have to be used, then include a dummy connector to plug the cable so that it can be located easily. When designing the product, try to minimize the flow of material waste, parts, etc, in the manufacturing operation. Finally, take packaging into account, select appropriate and safe packaging for the product

What is Injection Molding?

Injection Molding is a manufacturing process for producing parts in large volume. It is most typically used in mass-production processes where the same part is being created thousands or even millions of times in succession.

Why Use Injection Molding?

The principal advantage of injection molding is the ability to scale production en masse. Once the initial costs have been paid the price per unit during injection molded manufacturing is extremely low. The price also tends to drop drastically as more parts are produced. Other advantages are:

  • Injection Molding produces low scrap rates relative to traditional manufacturing processes like CNC machining which cut away substantial percentages of an original plastic block or sheet.
  • Injection Molding is very repeatable. That is, the second part you produce is going to be practically identical to the first one etc.