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Part Carriers
A common feature in all progressive stamping dies is the material that transports the parts from station-to-station as it passes through the die. This material is known by various terms, such as carrier, web, strip, tie, attachment, etc. In this instance, we will use the term carrier, of which there are five basic styles:
Solid carrier--All required work can be accomplished on the part without preliminary trimming. The part is cut off or blanked in the final operation.
Center carrier--The periphery of the part is trimmed; leaving only a narrow tie near the middle of the part. This permits work to be performed all around the part. A wide center carrier permits trimming only at the sides of the part.
Lance and carry at the center--The strip is lanced between parts, leaving a narrow area near the center to carry the parts. This eliminates scrap material between parts.
Outside carriers--The carriers are attached to the sides of the part so that work can be done to the center of the part.
One side carrier--The part is carried all the way or part of the way through the die with the carrier on one side only. This permits work on three sides of the part.
The type or shape of the carrier will vary depending on what the part requires as it progresses from station to station in the die. The stock width may be left solid if no part material motion is required during die closure or it can be notched to create one, two or even three carriers between the parts
The carriers can be straight, form a zig-zag pattern or have loops between the parts depending on where attachment points to the part are available or to accommodate whatever clearance may be required by the die tooling. As the part is formed, flanged or drawn into a shell, the carrier may have to move sideways or up and down as the die closes and opens.
When die operations cause the carrier to move, it usually will be required to flex or stretch. Regardless of carrier flexing, their key function is to move the parts close enough to the next station so that pilots, gauges and locators can put the parts into their precise location as the die closes.
If the carrier acquires a permanent stretch, the parts may progress too far to fit on the next station, or in the case that the die has two carriers, one carrier may develop permanent stretch with no stretch in the other carrier. This will create edge camber in the strip, causing it to veer to one side. This results in poor part location.
A stretched carrier can be shortened to its correct length by putting a dimple in the carrier. If a center carrier or one-sided carrier develops camber, the strip can be straightened by dimpling or scoring one side of the carrier. Construct the dimple and scoring punches so that they are easily adjusted sideways for position and vertically for depth.
as it is delivered from the coil can cause the strip to bind in the running gauges that guide the material during the feed cycle. This binding may cause the carriers to buckle, which results in short feeds. It often helps to relieve the guide edge of the gauges in between stations and have tighter gauge control at the work station.
Another option is to eliminate camber by trimming both sides of the material in the beginning of the die. By adding stops at the end of these trim notches they can be used as pitch control notches to prevent progression overfeed.
Optimum Carrier Profile
The optimum carrier profile is affected by some of the following conditions:
Space available between parts: Try to keep the carriers within the stock width and pitch required for the blank. If this is not possible then the designer must add to the width and/or the progression of the material to provide adequate carrier room.
Attachment points to the part: If two carriers are used, try to keep the profile and length of the carriers somewhat the same so that any effect of carrier flexing is close to being balanced.
Clearance for punch and die blocks: Punch blocks that extend below the stock or die blocks that extend above the stock when the die closes will require clearance in relation to the parts and the carriers. If a loop of the carrier interferes with blocks it may be possible to form the loop vertical to provide clearance.