Clinching has advantages over both riveting and spot welding.  There is no sparking or burning caused by spot welding.  Clinching can consistently fasten mismatched materials, a task at which spot welding often falls short.  Riveting requires fasteners which have a cost associated with each join.  Fasteners also require pre-punched holes to form and align during the fabrication process.

Process

Clinching is essentially a 4 step process.

1. The sheets are clamped together between a stripper plate and bottom plate.  This not only holds the metal in place during the forming, but also limits the area of metal drawn into the button.  This prevents deformation around the feature.
2. A punch tip is then forced down past the surface of the bottom sheet.  The punch is designed to draw the metals together without shearing or cracking the surface.
3. The punch tip then presses the sheets against a bottom die.  The pressure from the punch causes the metal to flow; the bottom die then directs the flow outwards forming the mushroom shape necessary to join the sheets.
4. Finally the stripper plate holds the sheets in place while the punch tip is retracted.  This process takes place in a single quick stroke.

Clinching Video

An excellent video from the makers of Tog-L-Lock showing the material flow of clinched sheet metal.  Here you can see the detail of the die tip being slightly dome shaped, assisting the lateral flow of the metal during the join.

Resources

• Engineering Standards Tog-L-Lock / Lance-N-Lock Information - Inspiration for this post, great information on clinching, terminology and technology.
• Overview of the TOX-Clinching Technology - Solid technical resources from one of the industry leaders in clinching technology.

A squaring arm is a versatile tool which attaches magnetically to the bottom Press Brake Die.  The arm provides a level surface with an adjustable edge to act as a stop for aligning parts which do not have enough contact area with the back gauge for proper alignment.   Because the squaring arm attaches magnetically to the v die setup time is quick and there’s no need for special tooling.   Unlike clamping across the bottom die the squaring arm does not interfere with the punch.   The only drawback with magnetic attachment is that it won’t connect with aluminum die blocks used for Urethane Tooling, to utilize the squaring arm you may need to modify the die block with a steel attachment.

An adjustable edge allows for the accurate bending of parts which do not fit squarely into the die.   The shelf incorporated with the arm can also allow an operator to position the part and remove their hands before engaging the brake.  This can make bending small parts safer.  For odd shaped parts and parts with down bends the opposite side of the shelf can still be used as a squaring edge.   Squaring arms come in a both left hand and right had design, denoting which side the arm is on.   This means that right handed operators will prefer the left handed version.

Squaring Arm Video

While is also displays their magnetic protractor this video shows the basic uses of a squaring arm.

Types of Punch Presses

Punch presses are typically first described by their frame.  The two most common frame types are C-Frame and Portal Frame.  C frame presses have the die set suspended at the end of a C shaped structure where portal frames are rectangular shaped with the die set suspended in the center.  Because of the additional support from the portal type most heavy duty industrial punches feature some variation of this design.  Most hand powered and mechanical presses have C-Frames.

C-Frame / Portal Frame

Much the same as a Brake Press, punch presses can be further classified by the machines method for delivering power to the punch tip.  The mechanisms for powering punch presses are: mechanical, pneumatic, hydraulic, and servo-electric.  Mechanical presses use a fly wheel, spun by an electric motor, to store energy.  When the operator engages the presses the fly wheel is connected to the punch tip through a clutch and mechanical linkage.  This method for powering presses is very slow and requires an operator to engage the linkage, lending itself to low tonnage presses.  Pneumatic and Hydraulic presses use air and water pressure, respectively, to drive the punch tip through the material.  These types of presses were at a time very popular but have generally been replaced by servo driven types.  Servo-electric presses use a heavy duty servo-motor to drive the punch at very high speeds with a great deal of control and positional accuracy.  Servo driven presses are much quieter than most of their counter parts and do not suffer from oil, air or hydraulic leaks.

Further characterizing punch presses are their capacities.  Work-bed size, tonnage rating and tool capacity are the three most distinguishing features of most presses.  Work bed size will determine the size of sheet that the press can process without re-positioning of the holding clamps.  A typical industrial press will be able to process a sheet in the area of 50” x 100”.  The die sets of punch presses are fixed, compared to that of a flying optic laser, so actuators need to move the sheet under the tool.  This happens to lend the C-Frame presses a slight advantage because there is no throat depth on one side of the machine, meaning a much wider sheet can be processed, though only a specific area can be punched.  Tonnage ratings will determine the thickness of sheet which can be processed, as well as the limitations of forming tools.  Tool capacity is simply how many stations of tooling the machine can handle.  Tooling capacity is also referred to as tool shop capacity.

Speed is determined by sheet movement speed and punch speed.  Sheet speed is typically rated without load or with a light load on the clamps.  Heavier sheets often are run at slower speeds to reduce wear on the bearings.  Punch speed is also determined by the thickness of metal being punched.   Holes per minute at 1” on center is often used to describe how many equally spaced holes the unit can produce on a given sheet size.

Other distinguishing features are safety features, supported tool types, bed type and software controls.

Punch Press Video

Standard break down of tooling:

• 3.937” (100 mm) Left and Right Ear
• .394” (10 mm)
• .591” (15 mm)
• .787” (20 mm)
• 1.575” (40 mm)
• 1.969 ” (50 mm)
• 7.874” (200 mm)
• 11.810” (300 mm)

In addition most manufacturers offer a 16.34” (415 mm) ‘Short’ Section and a 32.87” (835 mm) ‘Long’ Section.

Horn Punches

A horn, ear, dog leg punch all refer to the punches which are relieved for bending parts which have return flanges on the sides of the part.  The punches allow a clearance, similar to Window Punch which allows you to bend closed in boxes.  Typically every sectionalized set will contain a left and a right horn.  These punches can be further relieved for special application though this increases the risk of crowning on the extended edge and may necessitate Shimming.

Curls come in two basic forms, off center and on center rolls.  Off center rolls have the center of the roll above the original plane of the sheet metal. On center rolls will have the center of the roll in line with the plane of the sheet metal.

The type of curl you produced is a matter of design intent and the machinery available. As we will discuss below the process of forming a curl is different for each type of fabrication machine.  Because of this certain machines will lend themselves towards one style or another.

Forming A Sheet Metal Curl

How a curl is formed depends entirely on the type of machinery you wish to use. Curls can be fabricated through roll forming, stamping, leaf bending, and on a traditional press brake.  Each machine will have its own set of tooling for achieving the curl.  Here we will be discussing the fabrication and tooling methods for forming on a leaf bender and press brake.

Forming a Curl on a Panel Bender

Curling on a panel or leaf bender is often limited to off center curls because most panel benders do not have tooling profiles which can create the necessary down bend to put the curl on center.  Off center rolls however are very easily formed on this type of machine.  The desired radius is created by Step Bending a progressively larger radius into the sheet, beginning with the desired curl radius minus the material thickness, and ending with the desired curl radius.  The smaller radius is formed first to allow the material to finish inside itself.  The process of step bending involves producing very small bends in very close to each other, and while the finished bend is technically a polygon, it’s often impossible to detect the steps if they are formed correctly. For lighter gauges a hand operated panel bender can be the most affordable method for creating a curl.

Forming a Curl on a Brake Press

To curl sheet metal on a Brake Press specialized tooling is required.  Most curls are formed in three stages and some setups require two tooling setups with specialized tooling for each stage.  The first 2 stages form the curves required to form the curl, and the third stage closes the curl.  A locating notch is typical for this type of tooling to ensure that the first and second stages are bent in the correct location.  Below is a typical two setup, three stage tooling.

Because of this the tooling is typically unbalanced, meaning the tonnage isn’t evenly distributed front to back, so stabilizing features are sometimes incorporated.  When a stabilizing bar is used it allows for the two stages to be combined into one set of tooling.  Below is an example of a one setup , three stage tooling.