Lifters are used primarily for relieving internal undercuts or for zero draft internal faces. Their motion is driven by the molding press pushing on the ejector plates. A simple side action lifter withdraws at 90 degrees to the line of draw, simultaneous with ejection. The angle of the lifter passing through the core frequently confuses the novice into thinking that it pulls the feature at an angle. Relative to the core the lifter indeed moves at an angle. Relative to the part however a lifter moves directly sideways because the part is being ejected forward at the same rate as the lifter.
Having said all that however, it is possible to run a lifter at a small angle to the part, but this requires special hardware. These variants will be discussed later.
- Draft must be altered in the locale of the lifter. The lifter will be pulling sideways so draft in this area must be oriented in the lifters line of draw.
- Features such as ribs and bosses must not be placed in the way of lifter motion. Depending upon the size of your lifted feature you must allow for three things, the lifter body, lifter stroke, and 0.050" wiggle room to the next feature. These three requirements really depend upon many factors including the overall size of your part, the depth of undercut to be pulled, shape of the feature that you are pulling and the style of lifter used. As a rule of thumb however, if you are just pulling a typical hook or snap, leave 1.250" of room for lifter body, stroke, and clearance.
Similar to conventional lifter but moves at an upward angle relative to the part. Feature angle limit is 10 degrees. Determine the angle at which your lifter must travel and draft the feature relative to that vector.
Similar to conventional lifter but moves at a downward angle relative to the part. Feature angle limit is 10 degrees.Determine the angle at which your lifter must travel and draft the feature relative to that vector.
Straight up lifters
Track straight up with the part just like an ejector pin. The press operator must then pull the part off by hand. Best when used on simple features. Use liberal draft. Operator must be able to release the part by shifting it in one direction only. Risks include human damage to the part, and slower, irregular cycle times.
Very limited in depth of undercut and location. Good for small spaces however. Some durability issues. Recommended as a last resort only.
Drag along lifter
-El Cheapo. O.K. for prototype tools or those built in third world countries. Requires that the cavity side return it to its home position.