Sheet Metal Working
Chapter 20 of Fundamental of Modern Manufacturing
Mikell P. Groover
Contents
20.1 Cutting Operations
20.1.1 Shearing, Blanking, and Punching
20.1.2 Engineering Analysis of Sheet-Metal Cutting
20.1.3 Other Sheet-Metal-Cutting Operations
20.2 Bending Operations
20.2.1 V-Bending and Edge Bending
20.2.2 Engineering Analysis of Bending
20.2.3 Other Bending and Forming Operations
20.3 Drawing
20.3.1 Mechanics of Drawing
20.3.2 Engineering Analysis of Drawing
20.3.3 Other Drawing Operations
20.3.4 Defects in Drawing
20.4 Other Sheet-Metal-Forming Operations
20.4.1 Operations Performed with Metal Tooling
20.4.2 Rubber Forming Processes
20.5 Dies and Presses for Sheet-Metal Processes
20.5.1 Dies
20.5.2 Presses
20.6 Sheet-Metal Operations Not Performed on Presses
20.6.1 Stretch Forming
20.6.2 Roll Bending and Roll Forming
20.6.3 Spinning
20.6.4 High-Energy-Rate Forming
20.7 Bending of Tube Stock
Sheet metalworking includes cutting and forming operations performed on relatively thin sheets of metal. Typical sheet-metal thicknesses are between 0.4 mm (1/64 in) and 6 mm (1/4 in). When thickness exceeds about 6 mm, the stock is usually referred to as plate. The most commonly used sheet metal is low carbon steel (0.06%–0.15% C typical). Its low cost and good formability, combined with sufficient strength for most product applications, make it ideal as a starting material.
Industrial products that include sheet or plate metal parts: automobile and truck bodies, airplanes, railway cars, locomotives, farm and construction equipment, appliances, office furniture,
and more. These products have sheet-metal exteriors and many internal sheet metal components .
Sheet metal parts are generally characterized by high strength, good dimensional accuracy, good surface finish, and relatively low cost.
Most sheet-metal operations are performed on machine tools called presses. The term stamping press is used to distinguish these presses from forging and extrusion.
TYPE OF PRESSES
Presses are classified based upon the method of operation method of power source method of activation of slide and number of slides in action.
1. Method of Operation
(i) Arbor Press. It is a hand operated press. It combines the principle of lever with pinions to a related rack build into the ram. They are used where a very limited no. of production of parts is required.
(ii) Foot Press. It is also manual operated press. Most of the presses have foot action in their operating mechanism.
(iii) Open back inclinable press. It is a power operated press. They are having bench or floor models.
2. Method of Power Sources
(i) Manual presses
(ii) Mechanical power presses
(iii) Hydraulic presses.
(iv) Pnuematic presses
3. Method of Activation of Slide
(i) Crank shaft presses
(ii) Knuckle joint presses
(iii) Toggle presses
4. Number of Slides in Action
(i) single action presses
(ii) Double action presses
(iii Triple action
NPTEL Lecture 7 - PRESSES FOR SHEET METAL WORKING
NPTELMechanical EngineeringManufacturing Processes
https://nptel.ac.in/courses/112107144/7
Lecture 4 - FORMABILITY OF SHEET METAL
https://nptel.ac.in/courses/112107144/4
Lecture 6 - SHEET METAL PROCESSES
https://nptel.ac.in/courses/112107144/6
Lecture 8 - DIE AND PUNCH
https://nptel.ac.in/courses/112107144/8
Metal Press Work - YouTube Video
Uploaded by Engineering Education Channel
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https://www.youtube.com/watch?v=aUhvo0om1q0
PRESS OPERATION
Sheet metal process planner has to know certain fundamentals specifications of press machine. Some of them are press tonnages, stroke of the press, die area, shut height etc.,
Press tonnage
The tonnage of a mechanical press is equal to the shear strength of the crankshaft metal multiplied by the area of the crankshaft bearings.
The tonnage of a hydraulic press is the area multiplied by the oil pressure in the cylinder.
It indicates the amount of pressure in tonnes that a press exerts on work safely and is used for rating a press. The press may exist in various capacities of tonnes varying from 5, 10, 20, 32, 50, 75, 200, 500 tons to tackle the sheet metal operation using proper die in press.
Press stroke:
It is the reciprocating motion of a press slide. It is adjustable on a hydraulic press.
Die area: It is the available surface for mounting punches and die components
Shut height
It is the distance from the top of the bed to the bottom of the slide when stroke down and the adjustment up. The shut height of the die must be equal to or less than the shut height of the press.
Die shut height = Punch shoe thickness + Die show thickness + Die steel height + Punch
steel Height-bypass of steels.
The by-pass of steels may be taken as from 3 mm to 6 mm.
Sheet Metal Operations
1. Shearing. It takes place in the form of a cut when punch strikes and enters in the sheet placed on die. The quality of the cut surface is greatly influenced by the clearance between the two shearing edges of the punch and dies.
2. Cutting. It means severing a piece from a strip or sheet with a cut along a single line using suitable punch and die of press tool in press machine.
3. Parting. It signifies that scrap is removed between the two pieces to part them using suitable punch and die of press tool in press machine.
4. Blanking. It is a operation in which the punch removes a portion of material called blank from the strip of sheet metal of the necessary thickness and width using suitable punch and die of press tool in press machine.
5. Punching. It is the operation of producing circular holes on a sheet metal by a punch and die. The material punched out is removed as waste. Piercing, on the other hand, is the process of producing holes of any desired shape in the part or sheet using suitable punch and die of press tool in press machine.
6. Notching. It is a process to cut a specified shape of metal from the side or edge of the stock using suitable punch and die.
7. Slitting. When shearing is conducted along a line, the process is referred to as slitting. It cuts the metal sheet lengthwise using suitable punch and die of press tool in press machine.
8. Lancing. It makes a cut part way across a sheet and creates a bend along the cut using suitable punch and die.
9. Nibbling. It is an operation of cutting any shape from sheet metal without special tools. It is done on a nibbling machine.
10. Trimming. It is the operation of cutting away excess metal in a flange or flash from a sheet metal part using suitable punch and die of press tool in press machine.
11. Bending. Bending is the operation of deforming a sheet around a straight axis. The neutral plane lies on this straight axis. In bending all sheet material are stressed beyond the elastic limit in tension on the outside and in compression on the inside of the bend. There is only one line, the natural line that retains its original length. The neutral axis lies at a distance of 30 to 50% of thickness of the sheet from the inside of the bend. Stretching of the sheet metal on the outside makes the stock thinner. Bending is sometimes called as forming, which involves angle bending, roll bending, roll forming, seaming and spinning.
MACHINES USED IN SHEET METAL SHOP
The machines, which are in use to perform different operations on metal sheets, are as follows:
1. Shearing machine
2. Bending machine
3. Folding machine
4. Grooving machine
5. Peining machine
6. Beading machine
7. Swaging machine
8. Burring machine
9. Double seaming machine
Many special purpose machines are developed and fabricated to suit particular kinds of work for mass production of identical parts at lower cost.
Shearing machine
A shearing machine consists of a base or frame, which can be conveniently fixed on a bench in any position as desired. Two shearing blades are provided in the machine. One called the fixed blade is rigidly fixed with the frame whereas the other known as movable blade is operated by means of the hand lever provided at the rear. In operation, the metal sheet is placed between the shear blades in such a way that the markings of the layout come exactly under the cutting edge of the upper blade. Out of the two blades one is fixed and the other moveable. When the lever is pulled by the operator the lower blade rises and thus the metal sheet is cut. This particular provision enables the metal sheet to be locked against the upper blade during the operation on account of the circular motion of the hand lever. With the result, the metal sheet is prevented from being distorted.
Folding machines are used for bending and folding the edges of metal plates to form
the joint at the seam. Bending machines or bending rollers, as they are better known, are
used for shaping metal sheets into cylindrical objects. The machine consists of three rollers.
These rollers have different adjustments indifferent types of machines. In some-machines
two rollers at the bottom have fixed position and the third one (top roller) can be adjusted
in vertical direction to adjust the pressure and give the required curvature to the sheet.
A still better control is obtained by having two rollers exactly one over the other, out of
which the bottom roller is fixed and the top roller can be adjusted vertically to suit the
thickness of the sheet and the pressure required for rolling. The third roller, called radius
roller can be moved up and down to provide the desired curvature. Improved designs of
these machines are available which contain the rollers, which have grooves of various
shapes and sizes to form corresponding shapes in metal sheets. Conical shaped rollers are
used for tapered cylindrical articles. Similarly other machines named above are used to
perform different operations after which they are named.
Burring machine
Burring machine is used to make a burr on the edges of the bottom and covers. Burr is the starting of the seam. Double seaming machine is used for double seaming flat bottoms on straight or flared cylindrical pieces.
Various types of press machines with different capacities are used for mass production of sheet metal components. These are equipped with different kind of press tools or dies. These are commonly employed for fast and accurate processing of sheet metal work.
Industrial Engineering - Productivity Science
Process parameters in sheet-metal cutting are clearance between punch and die, stock thickness, type of metal and its strength, and length of the cut. (Groover, Section 20.1.2)
Die Basics 101: Intro to stamping
https://www.thefabricator.com/article/stamping/die-basics-101-intro-to-stamping
Getting to Production Faster with 3D-Printed Press Brake Tooling
A case study from Centerline Engineered Solutions demonstrates that a 3D-printed die and punch can withstand press brake forces, providing a cheaper, faster path to production.
https://www.additivemanufacturing.media/blog/post/getting-to-production-faster-with-3d-printed-press-brake-tooling
https://www.additivemanufacturing.media/blog/post/getting-to-production-faster-with-3d-printed-press-brake-tooling
Sheet Metal Stamping Dies and Processes - SME Training Guide - You can download
https://www.sme.org/study-guides
Punch Press Dies – Set Up and Working
https://www.eigenengineering.com/punch-press-dies-set-up-and-working-in-the-manufacturing-industry/
(+91) 80 61111300| info@eigenengineering.com
Eigen – USA
Address - 1:
4201 Military Highway
McAllen, Texas 78503 USA.
Phone : +1 248 933 4593.
Address - 2:
409 Rivanna Lane
Greenville, SC 29607.
Phone : +1 248 933 4593
Eigen
KDDL Ltd. Unit Eigen
No.55-A, Hunachur Village, Jala Hobli,
Yelahanka Taluk, Bangalore North
Near Kiadb Aerospace Park
Bangalore, Karnataka 562149
Phone: (+91) 80 61111300
Ext: 312
Email: info@eigenengineering.com
What is metal stamping? - The Basics of Metal Stamping
https://www.esict.com/what-is-metal-stamping/
Understanding Metal Stamping
https://www.thomasnet.com/articles/custom-manufacturing-fabricating/understanding-metal-stamping/
Updated on 8 Jan 2021 12 August 2019, 1 August 2019
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