【正文】 w of the die design at the location the strip will be for the first press stroke. Then the paper is marked with all of the operations that will be performed at the first die stationfor example, notching and punching. The paper strip then is moved to the second station on the drawing and the operations for both the first and second stations are marked. This process is repeated through all the die stations to illustrate what the real part strip will look like when it is started into the die and helps determine the adequacy of gauges and lifters.Flexible Part CarriersTo transport the strip from one station to the next in a progressive die, some material must be left between the parts on the strip. This carrier material may be solid across the width of the strip, or may be one or more narrow ribbons of material, see part carriers sidebar.Many parts require the edge of the blank to flow inward during flanging, forming or drawing operations. This may require the carrier to move sideways or flex vertically, or both, during the die operation. A flexible loop must be provided in the carrier to allow flexing and movement of the blank without pulling the adjacent parts out of position.Another concern is the vertical breathing of parts in die stations during the closing and opening of the die in the press stroke. For example, vertical breathing takes place between the draw stations of parts requiring more than one draw to plete the part. Vertical breathing also occurs when a flange is formed up in a progressive die station that is adjacent to stations that use upper pressure pads to hold the adjacent parts down.It is important to consider the flexing of the carrier during the upstroke of the press as well as during the downstroke because the action may be different. This can be simulated in the design stage by making an outline of the crosssection of the part, the pressure pads and the stationarymounted steels on separate sheets of paper and then placing these sheets on top of each other in layers over the die section views. These sheets then are moved down in relation to each other to simulate how the upper die would close during the press downstroke. This will show the relative position of the part as the die closes and during the reverse action as the die ram opens.A mon feature in all progressive stamping dies is the material that transports the parts from stationtostation 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 carrierAll required work can be acplished on the part without preliminary trimming. The part is cut off or blanked in the final operation.Center carrierThe 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 centerThe strip is lanced between parts, leaving a narrow area near the center to carry the parts. This eliminates scrap material between parts.Outside carriersThe carriers are attached to the sides of the part so that work can be done to the center of the part.One side carrierThe 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 zigzag pattern or have loops between the parts depending on where attachment points to the part are available or to acmodate 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 onesided 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.Edge camber of the material 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 ProfileThe 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 designe