Optimizing Progressive Die Design for Cost-Effective Manufacturing

Introduction

Progressive dies are widely used for mass production of sheet metal components due to its high productivity, high precision and relatively economic cost in terms of per piece of product [1]. A die is a specialized tool used in manufacturing industries to cut or shape materials mostly using a press. A progressive die has a series of operations. At each stations, an operation is performed on a work piece during a stroke of the press. Between strokes the piece in the metal strip is transferred to the next station.

A finished work piece is made at each station of the press. While the piercing punch cuts a hole in stroke , the blanking punch blanks out a portion of the metal in which a hole had been pierced at a previous station. A progressive die is a multiple station die in which the former operation is piercing and it is followed by blanking. In both operations a finite volume of metal is removed from the sheet metal If the final product is removed portion then the operation is known as blanking , if pierced sheet metal is the product then the operation is known as piercing.

Literature Survey

Progressive is an economical way to produce a metal parts with suitable of characteristics including strength, ductility, and wear resistance. Development of strip layout, design and selection of die components and accessories , selection of die materials and die modeling are the major activities for designing a progressive die [2] . This research deals with the two stage progressive die has been designed for the washer manufacturing.

The material of part is mild steel. So here D2 type of steel is used for punch and die. It has more hardness and strength than the mild steel. By using this material to increase the tool life of progressive die. Punch and die both are made of high speed steel. Die is the part where strength and wear resistance both properties are required [3].

Strip layout design for progressive die is to arrange layout of the operations and subsequently determining the number of stations required. For design of strip layout , the die designer determines the sheet metal operations required for manufacturing the parts , sequencing of operations, selection of piloting method , number of stations required and the operations stamped at each station of progressive die . Strip layout is determined by the shape of a part and its technical requirements. It is generally governed by the geometrical feature of the part , tolerance on dimensions of the part , directions of sharp edge of stock strip and other technical requirements.

One important task is strip layout but it is very difficult task in design. Strip layout is an important step in the planning stage of sheet metal work on progressive die . It is an experience driven activity and the quality of strip layout is highly depend on the knowledge and skill of die design. It has the productivity , accuracy ,cost and quality of a die mainly depend on the strip layout. Another important factor is piloting . The strip must be positioned accurately in each stations so that the operations can be performed at the proper station or location . The task of selection of piloting scheme should be viewed as interdependent task in the strip layout design process .A strip layout design system should support direct piloting , semi direct piloting and indirect piloting scheme.

Punch is an important part of the press tool. It is fastened to the ram and forced into the die where work piece to be processed is supported. The diverse nature of products produced by progressive dies demands a high level of knowledge on the part of the die designer that can only be achieved through years of practical experience [4]. Die is a work holding device , designed specifically for a particular design of a product. Die is rigidly held on the base of the press. Die carries an opening which is perfectly aligned with the punch and its movement. Both die and punch work together as a unit and this is called as die set.

Progressive die metal stamping is based on the continuous feed of material through the different die stations of a tool. The nature of the process allows you to create more parts in a shorter period of time when compared with traditional fabrication or machining. For high volume parts, progressive stamping provides the lowest cycle times per part. Die stamping is a metal working method that can encompass punching , coining, bending, and other ways of modifying metal to produce your desired end part shape. The vast majority of material is used , hence less scrap is produced. Progressive die metal stamping may provide the most cost effective material option for manufacturing your parts.

With the development of new and high strength materials comes a dramatically increased failure rate of cutting punches. A broken punch if carried through an automated system such as a transfer or progressive die can result in severe die damage , not to mention a great deal of downtime and the frustration . numerous factors contributes to the premature failure or breakage of piercing and cutting punches. Two of the most common contributes are operator error and incorrect cutting clearance.

Most die building and stamping shops have an across the board cutting clearance that they use for all of their cutting applications. Most of the time it is about 10 percent of the metals thickness per side. If the shop is stamping mostly aluminum it might be about 8 percent per side. With stainless steel, 12 percent per side. Although these percentages are good rules of thumb , they are certainly not always the best clearance for every cutting applications.

Design Calculations

Capacity

Tonnage capacity = 7.06 tons.

Where,

Thickness of strip = 2mm,

Perimeter = 176.54mm,

Ultimate shear strength of mild steel =200mpa.

Fc = (p*t*fs)/10000 tons where,

P = perimeters,

T = thickness of strip,

Fc = ultimate shear strength

Fc = (176.52*3*200)/10000

=7.06 t

· P = (4 x L) + (2 x π x r) mm

Where,

Perimeter of square = 4 x L

Perimeter of circle = 2 x π x r

Perimeter of square = 4 x L

= 4*30

=120mm

Perimeter of circle = 2 x π x r

=2 x 3.14 x 9

=56.52mm

Total perimeter = 120 + 56.52

=176.52 mm

Percentage stock utilization

Blank area = L x L – (π x r x r)

=30 x 30 – (3.14 x 9 x 9)

=645.53 mm2

Total area of strip = {(n x 30) +(n+1)4} x {(2 x 3) + 30}

=118908 mm2

Percentage of stock utilization = (blank area x number of blanks)/total area of strip x 100

= (645.53 x 100)/118908 x 100

= 54.28 %

Shear Calculation

Required cutting force to cut the square object is 7.06 tons

Require press tonnage capacity is

= 7.06*1.2 (take factor of safety)

= 8.472 tons

Available press is 10 tons so it safe for using and get require accuracy.

If we have available only 5 tons press then we go for punch with shear angle take factor of safety = 5/1.2

= 4.16 tons. f

= k * p

( k = T x P / S )

where,

f = maximum cutting force

t= thickness of strip

s = shear in mm

p = force require to cut the objects

4.16 x 104 = (2 x .25 )/s x 7.06 x 104 s

S = 0.848 mm

Future work

• We will manufacture progressive die as per industry requirement .
• We will optimize strip layout design as possible.
• We will manufacture square washer of dimension 30x30 mm . And hole size of 50 mm .

Results and Discussion

The application of stock utilization concepts, strip layout optimization, and shear angle calculation demonstrates the potential to produce square washers efficiently. Material selection emerges as a critical factor in cost optimization, with design modifications proposed to reduce die costs by up to 20%. The study anticipates a reduction in scrap percentage through improved strip layout design.

Conclusion

The concept of stock utilization, strip layout , shear angle calculation has been applied to produce a square washer with the help of progressive die. Material selection of the vital criteria in optimizing cost of the die. The overall cost of die can also be reduced by efficient design of strip layout and its automation. Design calculations were done accurately proving enough allowances wherever required in order to avoid slug pulling. Hence the overall cost of the die is expected to reduced by 20 %. ,if the die is designed as per the guidelines presented in this paper.

References

1. Kumar, S., & Singh, R. (2004). A low cost knowledge base system framework for progressive die design. Journal of Materials Processing Technology, 153-154, 958–964. doi:10.1016/j.jmatprotec.2004.04.2362
2. Y.K.D.V. Prasad, Some studies on problems associated with automated design of cutting dies for sheet metal, Ph.D. Thesis, Department of Mechanical Engineering, IIT, Bombay, India, 1992.
3. SELECTION OF DIE MATERIALS AND SURFACE TREATMENTS FOR INCREASING DIE LIFE IN HOT AND WARM FORGING Paper no 644-FIA Tech Conference,(April 2011) pp 1-10
4. M.C. Cakir, O. Irfan, K. Cavdar, An expert system approach
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8. H. S. Ismail, S. T. Chen and K. K. B. Hon. ‘Feature-Based Design of Progressive Press Tools.’InternationalJournal of Machine Tools and Manufacture, Vol. 36, Issue3, pp. 367-378, 1996.