|
|
The Deep Draw Process
History of Deep Drawing and "Eyelet" Machines
The eyelet industry was born out of the brass industry, which was the major industry in Waterbury, CT and the general area, the Naugatuck Valley, in the 19th and early 20th centuries. For nearly a century, Waterbury was known as the "brass city of the world". 
The brass mills and industry started in 1802 and by the time of it's height in 1880, three fourths of all rolling and manufacture of brass in the country was being done in the Naugatuck Valley. In the late 18th century agriculture in the rocky and sometimes swampy areas around Waterbury was giving way to the Industrial Revolution. The Naugatuck River and Mad River once used to power the sawmills and gristmills, were being eyed as power sources for shops and waterways to markets. Farmer's sons turned into craftsmen using their hands to form metal and wood rather than till the earth. In the Waterbury area two businesses began the first steps into the Industrial Revolution. The clock field was pioneered by Eli Terry in 1793, when Abel and Levi Porter began producing metal buttons in 1802. Both industries required brass, which was very malleable for the crude tools of the day. The formation of buttons became more sophisticated as the original Porter business was sold to Frederick Leavenworth, David Hayden, and J.M. Scovill in 1811. This company eventually became the Scovill Manufacturing Company.
In the early 1800s the growing need for forming brass evolved because of the introduction of gas lighting. The demand for tubing and lamps for public and private gas lighting became another offshoot of brass forming technology.
The need for more workable forms of brass led Aaron Benedict and Alfred Platt to import heavy rolls from England in 1824 and start the Platt Mills Company. 
These rolls were utilized to make brass into the more versatile form of sheet. This growing technology for forming brass again came into demand for wire used for electricity, telegraph and telephones.
To compete with more refined methods of brass formation in England, an entire industry of specialized machines was born in the Waterbury area to fabricate brass. This industry was pioneered by Eli and Frank Manville in the mid 1800's. Eli Manville was considered a natural master mechanic and genius who had gained various experience by working in many of the local factories. He founded the Eli Manville Company in 1878 and invented such machines as the "Four Slide" and "Hendey Planer" and "Shaper". The company continued under son Bob and eventually was sold. While in existence, the company built the first "eyelet" machine, or as it is more correctly called, the transfer press. The machine was built to fabricate brass into reinforcing eyelets for shoes, tents, and corsets. Over the years the versatility of the machine became evident and further
advances in tool steel and tool design made way for the production of thousands of various shapes and forms. The Waterbury Farrel Company,
continued the tradition of the Manville Company and further refined the mechanical workings of the transfer press.
The last of the large brass fabricators have all but left the Naugatuck Valley. However, its offshoot, the "eyelet" industry and the many eyelet craftsmen, have survived to form the hub of a very unique and prosperous industry. Although some eyelet operations exist outside of this geographic region, the talent for this field is overwhelmingly settled in the Naugatuck Valley, the birthplace of eyelet technology.
Fundamentals of Deep Drawing
What is Deep Drawing?
Deep drawing refers to the process of drawing metal where the depth of the formed cup is equal to or greater than the radius of the cup. There are two basic types of equipment on which Deep Drawing can be performed, Transfer Presses and Progressive Presses. The fundamentals of the drawing process are the same on both types of equipment, but the method that the part is carried through the process differs. Transfer presses are multiple plunger power presses, with independent punches and dies for each plunger station. A blank is cut from the strip metal in the first operation and then carried through the other operations with the use of a cam driven slide with fingers. This is also known as free blanking. In the Progressive Press process the part remains attached to the strip metal and is transferred or carried through the operations via the strip.
When completely drawn to size, the shells are "harder" than the original material due to the effect of cold working the material. However, this increase in hardness varies from the top to the bottom of a shell. In essence the more work done to the material the "harder" the material becomes.
Eyelet Machines or Transfer Presses
The transfer press process starts with a strip fed into the machine at the first, or blank station. The blank for the 
shell to be drawn is cut from the strip and pushed down into the transfer slide. The transfer slide, moving perpendicularly to the strip feed direction, carries the blank to the first draw, or the cupping station. Here, the blank is drawn to a cup shape. Meanwhile the transfer slide returns to its original position to accept the next blank.
When the transfer slide is in position to receive a new blank, transfer fingers attached to the slide position themselves to carry the newly drawn cup from the first blank. Now, the movement of the slide not only carries the blank to the cupping station, but the first drawn cup is transferred to the next station to be redrawn. This process is continued as the transfer slide reciprocates back and forth with its spring-loaded fingers, picking and placing the parts from station to station until the slide is "filled". Then, with every revolution of the machine, a finished part is produced. Shells produced in this manner do not require annealing. Once the between redraw stations machine is running, the heat generated by the drawing operations aids in the flow of the material.
Plungers on a transfer press are individually cam operated, each having its own down-stroke cam and its own lifter cam. These cams are mounted alternately on the upper cam shaft. A cam roller bearing is mounted at the top of each plunger. Tool shut height is adjustable through the use of a keyway located beneath the cam roller bearing. The figure shown illustrates the operation of a Waterbury Farrel Individual Cam Operated Plunger Machine.
The upward motion of the plunger is controlled by the lifter cam which operates against a horizontal lifter arm. The lifter cam has two areas of lift with an intervening dwell. The lifter arm position on the lifter rod is adjustable. When the horizontal lifter arm is adjusted away from the cam, contact with the cam will occur later in cam rotation, providing a shorter first stroke. Longer first lift strokes are provided by setting the lifter arm closer to the cam. The first lift is adjusted to provide full extraction of the part from the die for any amount of engagement in the die up to maximum depth of the drawn shell.
The dwell area of the lifter cam allows the punch to remain stationary while fully inserted in the part, and slightly above the top of the die. During this dwell the transfer fingers grip the part.
When the second lift begins, the part is prevented from moving upward with the punch by a stripper sleeve and is stripped from the punch. The part remains in the transfer fingers ready for movement to the next station. All parts are transferred to the next station at the same time. Transfer timing is fixed and needs no adjustment.
Progressive Presses
A progressive press functions fundamentally the same as a transfer press. The fundamentals of the drawing process remain the same; however, the strip acts as the 
transfer mechanism. A progressive strip is fed into the press parallel to the tool progression and the finished part is not cut from the strip until it is completely formed. Another major difference is in the tooling. Tools are all contained in a large plate and there are no independently operated plungers. There is a female and a male die plate. The timing of the tooling is controlled with in the die plate by adjusting the heights of the tools. There are no individual cams to adjust, the tools come together all at the same time. Tooling is much more expensive than for transfer presses, due to the intricate design. However, the cost may be offset by the ability of progressive presses to produce more parts per minute than the transfer presses can. To the right is a diagram of a progressive tool and strip.
Eyelet Theory
Many factors must be taken into account when designing a deep drawn part. Including but not limited to: Material type and thickness, Part size and shape, Press Speed, Draw Ratio, Lubricants, N and R values of the metal, Punch and Die surface finishes, etc.
The N value of metal is the work hardening exponent and tells of the metals ability to stretch. The R value of metal is the plastic strain ratio and tells of the metals ability to flow or draw.
The draw ratio of a drawn part refers to the size of the punch to the size of the blank. 
If a parts diameter is too small to do in one draw, draw reductions, or redraws, will be necessary. They too must fall within acceptable draw ratios. It is important to note that all of the material necessary to make the finished part must be in the first draw. This is done by calculating the surface area of the finished part, and adding additional material if the part is to be clipped, trimmed, or pierced. The calculated surface area is then converted into a flat blank diameter.
Formula to solve for blank size of a cylindrical shell:
D = the square root of (d2 + 4dh)
D = shell diameter
H = height
D = Blank Diameter
To the right is a diagram of the forces at work on a blank when it is cupped:
Operation and Station Functions
For some examples of how different characteristics are formed on an eyelet machine, download this pdf .