9a Case Studies

Chapter 9

Some Case Studies

Chapter 9

Some Case Studies

Piercing, Semi notching and Parting in a Progressive Die

An adjustable arm for a shoe tree (see fig.) was made in a progressive die from 0.8 mm. thick cold rolled 1008 steel coil with a No. 2 finish and No. 3 edge purchased to the exact developed width of the blank 35 mm. The resultant saving in material, high production rate and low per-piece labour cost were important in marketing this highly competitive, mass produced item. The strip development is shown in above figure. The step in making this part in the progressive die was: pierce 21 holes and semi notch, stamp trademark, part and form.

Piercing, Semi notching and Parting in a Progressive Die

No deburring, polishing, buffing or barrel finishing operations was needed on the subsequently plated part. The only preparation done before bright nickel plating was solvent cleaning. As a further economy measure, the coil stock was selected to average in the low end of thickness range. The production rate was 3500 pieces per hour in a 75-ton mechanical press. Setup time was 3 hr. Yearly production was about five million pieces in lots averaging 4,00,000 pieces. Typically, regrinding of the dies (D2 tool steel) was required oil lubricant was used.

Producing a Bracket in Large Quantities in a Progressive Die

Fig. shows a bracket and a strip development for producing it in a five station progressive die in a 75-ton mechanical press that had an a 100 mm stroke, an air-actuated stock feeder and an automatic oiler. Material from the bracket was coiled cold rolled low-carbon steel strip 2.4 mm. thick by 133 mm. wide in the NO. 2 (half-hard) temper.

The die was made of D2 tool steel and hardened to Rockwell C 58 to 60. Setup time was 1.5 hr. and the press was stopped for die maintenance at intervals of 15,000 pieces. Production was at the rate of 1,200 pieces per hour. Light paraffin oil was the lubricant used. Tolerance on the dimensions of all of the pierced holes was +0.050, -0.025 mm., and tolerance on the position of the square hole and the two rounded slots was ±0.125 mm.

Producing a Stator and Rotor in a Progressive Die

Station 1: Pierce pilot holes, rotor slots and rotor shaft hole.

Station 2: Pierce stator rivet holes and blank rotor. Station 3: Pierce stator slots. Station 4: Idle. Station 5: Blank stator

One of the common types of progressive die used in the electric motor field is five station die that produces a rotor lamination and a stator lamination with each stroke of the press as shown in fig. This die can be provided with carbide inserts for the punch and die sections. It has a spring-actuated guided stripper. The die components are mounted on a precision die set with ball bearing guide bushings and hardened guide pins. Slender punches are guided through the stripper by bushings. Usually, such a die has four active stations and one idle station.

Producing a Stator and Rotor in a Progressive Die

Strip layout for producing rotor and stator laminations in a progressive die. Rotor lamination was pierced and blanked, and stator lamination was notched and cut-off.

Station 1: Pierce rotor shaft hole and five holes in stator. Station 2: Pierce slots in rotor. Station 3: Idle. Station 4: Blank rotor. Station 5: Pierce cutout for stator windings. Station 6: Notch end counter of stator. Station 7: Idle. Station 8: Cut stator from strip.

Stator and rotor laminations shown in fig. were produced from 0.63 mm. thick M-22 silicon steel in a 60 ton press with 25 mm. stroke and 230 mm. maximum die space over the bolster. Shut height of the die was 225 mm. The 12-slot rotor was 40.2 mm. outside diameter and had a 9.5 mm. diameter center hole. A stator was 73 mm long by 55.6 mm. wide. Calculated blanking pressure was 38 tons, and over-all die size was 310 by 460 mm. The tungsten carbide die average 8,20,000 strokes per sharpening when operated at 200 strokes per minute. The life of tungsten carbide die was approximately 80 million parts of laminations.

Blanking and Piercing Large E and I Lamination

Progressive die strip layout for laminations difficult to produce from 0.1 mm. strip because of their shape and size.

Station 1: Pierce twelve holes. Station 2: Blanked through two I-shaped laminations. Station 3: Idle. Station 4: Blank one E-shaped lamination through the die; the other lamination slides off the end.

A punch-to-die clearance 0.005 mm. per side maintained in blanking and piercing the relatively large lamination shown in fig. A 100 ton press with 38 mm. stroke was used to produce two E-shaped and two I-shaped parts from M-7 (grain-oriented silicon steel) with each press stroke. A cutoff-type progressive carbide die, 510 by 1050 mm. in overall size was used, assembled in a custom made precision die set with a spring type guided stripper.

The I-shaped laminations were blanked through the die and slacked in a chute. One E-lamination was blanked through the die and slacked while the other slid off the end of the die into a chute. A progressive die design made for similar product with different size is shown in fig. on next page for study.

Blanking and Piercing Large E and I Lamination

Plan view of Progressive die for E and I shaped laminations

Blanking and Piercing Large E and I Lamination

Sectional Elevation view of Progressive die for E and I shaped laminations

Blanking and Piercing Large E and I Lamination

Sectional Endview of Progressive die for E and I shaped laminations

Use of Progressive Die for Drawing a Small Ferrule

Production of a small-flanged ferrule in a progressive die.

The production of a small-flanged ferrule in a five-station progressive die is shown in Fig. The cost pr piece by this method was 40% of that estimated for producing the part in three separate dies. This did not include cost of setup, which would be greater for three separate dies. The progressive die was made of D2 tool steel and was hardened to Rockwell C 60 to 62. A 35 ton press with a 25 mm. stroke and hand feed produced 1500 pieces per hour from 38 mm. wide coil stock. The die produced 10,000 parts before reconditioning was required. An automatic oiler supplied commercial drawing lubricant.

Redrawing a Spring Seat in a Progressive die

Drawing a mass-produced automatic spring seat in a progressive die.

The The spring seat shown in fig. was drawn in a progressive die in quantities of more than a million pieces per year. After cupping, three redraws were used to form the cup to shape, depth and diameter. The die was operated in a 100-ton mechanical press at60 mm. stroke per minute. Stock was cold rolled or 1010 steel 127 mm. wide by 2.4 mm. thick. Sulfurized oil was originally used as the lubricant, but it was found that water-soluble oil did the job and was easier to remove. The lubricant was applied by intermittent spraying.

Forming a channel-shape Clip in a Progressive Die

Strip development for progressive die forming of retaining clip.In the first station, the strip was held firmly against a rear stock guide and

trimmed along the front edge to a developed width of 56.3 mm. In addition to trimming in the first section, a 6.4 mm diameter hole was pierced and two notches, 4.8 by 21.8 mm., were cut, leaving a center carrier tab 12.7 mm. wide.In the next working station 3, two weld projections were embossed. Then in station 5, the two bottom flanges were bent 90° and the upper bends were partly completed. Final bending was done in station 6 and the part was cut off in station 8 by a slug-type punch. Stations 2, 4 and 7 were idle to make room for mounting the punch and die elements.

Forming a channel-shape Clip in a Progressive Die

Strip development for progressive die forming of retaining clip.In the first station, the strip was held firmly against a rear stock guide and

trimmed along the front edge to a developed width of 56.3 mm. In addition to trimming in the first section, a 6.4 mm diameter hole was pierced and two notches, 4.8 by 21.8 mm., were cut, leaving a center carrier tab 12.7 mm. wide.

In the next working station 3), two weld projections were embossed. Then in station 5, the two bottom flanges were bent 90° and the upper bends were partly completed. Final bending was done in station 6 and the part was cut off in station 8 by a slug-type punch. Stations 2, 4 and 7 were idle to make room for mounting the punch and die elements.

Nesting of Workpiece to Minimize Stock Waste

The operations in the three working stations were: pierce one pilot hole and two flange holes and notch the counter; bend two tab upward; and flange and cut off from the center connecting tab. The die was used in a 150-ton mechanical press that could make 50 strokes per minute. Allowing for setup and downtime. Production was 2,800 pieces per hour. A light mineral oil was the lubricant.

The die was made of W1 tool steel hardened to Rockwell C 58 to 60. The punch to die clearance for cutting elements was 6% of stock thickness per side. Annual production was 1,00,000 brackets.