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Engineering Study

Concept Part
What method is the best method to manufacture the part you are currently working on?
This engineering study takes a look at seven different methods to mold the above part. Each method offers its own solution to a problem that has many answers. Some methods offer cost savings while others may give part design flexibility.

Concept Part
The objective of this concept part explanation is to demonstrate different manufacturing methods to produce the same or a very similar multishot part. It will conclude by giving cost breakdowns on all options, including capital cost, cycle time, and ultimately piece part cost.

Below, you will find information on equipment, processes, and the transportation methods we used for this demonstration.

Injection Molding Machines
Equipped with two separate injection units. Both injection units are capable of filling at the same time, generally to two different positions in the mold.

A. Molds are generally molded then moved to a new location for the second shot. This allows cavities for second shot to be totally different than first shot. Versions one through five are four cavities for first and second shot. Version six is an eight cavity mold with only one cavity position.

B. Robotics are self descriptive. The robot picks the part off the first shot position and relocates the part into the second shot position.

Advantages: One-time capital cost.
Disadvantages: If the core you are relocating on is complicated, i.e. ribs and other part detail, the robot may be unable to place or force the part onto a new second shot core. Generally, higher scrap rates result because of misplaced and/or dropped parts.

Rotating Platen
Generally a function of the machine. Basically it is a turntable, a rotating plate mounted on or in the ejector platen of the press. On some machines, it is an integrated part of the press and the platen is machined to accommodate the rotating mechanisms. On smaller presses, it may be a separate transmission housing bolted onto the ejector platen.

A. The rotating platen applications are mostly used for over-molding\applications where the core would stay the same for both first and second shot. After first shot is molded the mold opens up, then the complete ejector half of the mold rotates 180 degrees, then the mold closes and second shot is molded over the top of first shot. This is typical for most of the over-mold and soft touch applications.

Advantages: This is a one-time capital investment. The turntable is capable of being utilized as the transportation method for many molds.
Disadvantages: When using a turntable, you cannot put a new core underneath first shot. This investment will not be useful if the part requires the features of a rotating stripper plate.

Rotating Stripper Plate (Indexing Plate)
Generally a function of the mold. Located in the center of the ejector half of the mold (where the sprue puller pin is generally located) is the center shaft that lifts and rotates the stripper plate. This shaft attaches to the back side of the stripper plate, opposite the parting line and goes through the "B" plate, any support plates, ejector housing and machine’s platen. The other end of the shaft may or may not be attached to the machine’s knock-out plate. The press knock-outs move the stripper plate forward. The center shaft then is rotated by either hydraulic motor or a rack and pinion mechanism.

Advantages: Rotary stripper plates are used when the part requires a new core for second shot. After lifting first shot off of the core with a stripper plate, you can rotate and relocate first shot onto a new core at the second shot position to create new geometry or new coring detail.
Disadvantages: Unlike a turntable, a rotating stripper plate is not capable of being utilized as the transportation method for many molds; the rotation is built into the tool.

Retracting Sleeve or Core Toggle
Generally a function of the mold. Sometimes referred to as core back. This usually requires an extra core pull sequence on the machine and a set of moving core plates.

Advantages: Lower capital cost and possibly cycle time reduction because there are no transportation requirements.
Disadvantages: Rarely usable because of part requirements or restrictions.