2 STRIP LAYOUT FOR BLANKING TOOLS. Choice of strip layout method.• Blanking tools produce blanks out of the strip or unit stock.• None of the edges of the strip or unit stock forms an edge of the blank.• Blanking is the most efficient and popular way of producing intricateand closely tolerated blanks.• The profile and accuracy built into the tool will be reproduced onthe blank.• In the strip layout, blanks can be positioned in different ways in the strip.
3 STRIP LAYOUTA strip layout represents the sequence of the logical, workable operations, which is to say a sequence of ideas.If this sequence of operations has error, the error will be surely emerge in a try out press.Factors to be considered while designing the layout are.Shape of the blank.Production requirement.Grain direction.Burr side.Stock material.
4 Production Requirement: Shape of the blank:The contour of the blank, decides the position of the strip.Some of the blanks are laid at an angle.Production Requirement:If production requirement is less, then material conservation is necessary.This must not increase the tool cost.Gang die may be suitable for the mass production.Grain Direction:The grains are found in the sheets when they are rolled.Bending the strip along the grain direction results in crack and fracture.Burr Side:It is a decisive factor in laying the strip.In blanking, burr is found on the punch side.In piercing ,burr is found on the die side.Stock Material:Every means is to be seen to conserve the stock material.A double pass layout would justify the cost of stock material conserved.
5 ECONOMY FACTOR:The designer should try out every possible means to attain a min 60% usage of any strip, without sacrificing the accuracy of the piece part.Economy Factor =Area of the blank x No of rows x 100Width of the strip x Pitch
7 TERMS USED IN STRIP LAYOUT Pitch Distance between two consecutive operations on a strip.Scrap bridgeThis is the portion of the material remaining after blanking operation between one edge of the strip and the cutout portion. The portion of material remaining between the two adjacent openings after blanking is also called as the scrap bridge.Front ScrapThis is the scrap bridge on that edge of the strip which is towards the operator.Back ScrapThis is the scrap bridge on that edge of the strip which is away from the operator
8 EXAMPLE:Calculate the economy factor to punch the mild steel washer in single row feeding. Outside diameter is 30mm, Inside diameter is 18mm and Thickness is 2mm
9 Area of blank x No. of rows x 100 pitch x strip width Scrap bridge width is = 1.2 s.Scrap bridge width = 1.2 x 2=2.4 mmPitch = = 32 mmStrip width = = 34.8 mmNumber of rows = oneArea of blank = Л D²4= Л 30²= mm²Area of blank x No. of rows x 100pitch x strip width
10 Calculate the economy factor to punch the same washer in double row feeding
11 Single row one pass layout • This is the most popular way of laying out the strip.• The blanks are arranged in a single row.• The strip is passed through the tool only once to punch out the blanks from it.• There are two possible ways of laying out this strip.
13 WIDE RUN • Wide run is more desirable due to the following reasons. • Shorter advance distance of the strip feeding promotes easy• More" blanks could be produced from a given length of strip comparedto narrow run.• Fewer number of strips are to be handled to produce a givennumber of blanks.• Narrow run is used when the grain direction of the piece parthas importance.
14 BLANKS HAVING AT LEAST TWO STRAIGHT PARALLEL EDGES. • In such cases the strip width should be equal to the distance between theparallel sides.• The blanks are produced by a cut off or parting operation.• If the blank has got two sets of parallel sides, a cut off operation is sufficientto produce the blanks.• But if the blank has got only one set of parallel sides, these sides becomethe sides of the stock strip and the other non-parallel sides are produced bya parting operation.
15 STRIP LAYOUT FOR CUT OFF AND PARTING • Cut off punch cuts with only one edge.• No scrap is produced.• A parting punch cuts with two opposite edges thereby producing a scrap.NOTCHING• Notching is a cutting operation for cutting off small portions from the edgeof a strip or a pre blanked component.
16 STRIP LAYOUT FOR CUT OFF • Cut off punch cuts with only one edge.• No scrap is produced.• A parting punch cuts with two opposite edges thereby producing ascrap.
17 • Trimming is an operation of cutting off material to alter the shape of the strip or blank.• In notching only a small area of the blank is cut off.• In trimming a larger area of material is removed.• Blank can be produced by combining notching, trimming and piercingoperations with cut off or parting operations.
18 BLANKS HAVING IRREGULAR CONTOUR • The following factors must be considered before determiningthe best method of positioning a blank in the strip.Contour.Minimum material wastage.Less tool cost.No scrap strip to handle which renders the production faster.Accuracy in strip width.Accuracy of the blank.Flatness.
19 CONTOUR.• If the blank has two parallel sides, it can be produced by cut off operation.• The advantages of cut off or parting operation are:• Minimum material wastage.• Less tool cost.• No scrap strip to handle.• Speeds up production.
20 ACCURACY IN STRIP WIDTH. • Sheared strips cannot be held to an accuracy closer than ± 0,2mm.• If the blank must be held to close limits on its width sides cutting off orparting cannot be employed.• When the blank dimensions are to be controlled to close limits itshould be produced with a blanking tool, regardless of the parallelsides it may contain.FLATNESS.• If the blank has to be flat, a blanking tool is preferred.• A blanking tool produce considerably flatter components than other tools.
21 SINGLE ROW TWO PASS METHOD • This strip layout demands the strip to be fed twice through the tool.• This is to achieve greater economy in stock material utilization.• A two pass tool requires two stops.• The stop used for the first pass should be removed or made to retractspring loaded stoppers) from the working surface so as not to interferewith the second pass.
22 • The front and back scrap as well as the scrap bridge should be wider than those for he single pass (about 50 to 100%).• Two pass layouts are justified only when the wastage is considerable andthe stock material is costly.
23 DOUBLE ROW LAYOUT.• Higher economy can be attained by positioning the blanks in double rows.
24 GANG DIES• A gang die consists of two or more similar sets of tool members so as toproduce 2 or more number of components during a single stroke of thepress ram.• A gang die eliminates the cumbersome process of double pass.• The higher tool cost will be off set by higher rate of production.• Gang dies are not recommended for very complex work.
25 ANGULAR LAYOUTSome of the piece parts will be require to be laid out to an angular position to make the layout more economical.