30-06-2012, 04:15 PM
SHEET METAL DESIGN HANDBOOK
Design-Handbook-Rev3(6).pdf (Size: 151.28 KB / Downloads: 283)
Forming Basics
Press brake forming-The fundamental advantage of a press brake as a forming tool is its
flexibility. By using standard vee-dies, cost savings can be realized through economical set-ups
and run times on small lots and prototypes. In addition to these considerations, using the
following guidelines will increase the manufacturability of designs for press brake forming.
Dimension the part in a single direction wherever possible. Because of the sequential nature of
the forming process, and the fact that dimensional variation is introduced at each bend,
dimensioning in a single direction parallels the process and helps to control tolerance
accumulation. Furthermore, allow a more generous bend tolerance (+/- .007”) as tighter
tolerances, while achievable, will result in higher costs.
Use consistent bend radius for all bends per part, when possible—it helps minimize setup
changes. Additionally, we prefer radii specs in fractions of an inch, as our tooling is sized
accordingly.
Generally, dimensioning should be done from a feature to an edge. Avoid feature-to-feature
dimensions over two or more planes. Feature-to-bend dimensions may require special fixtures or
gauging.
This also means that tolerances in the title block of a drawing may be unnecessarily restrictive for
certain dimensions and angles, while very appropriate for others.
Laser Cutting Basics
With very little set up time, no tooling and the advent of CAD to CAM production, lasers are often
utilized in prototyping and production parts. Well suited for intricate details and irregular contours,
additional economies can be obtained through the nesting of parts when laser cutting.
Tolerances – The feature to feature tolerance on for the laser cutter is +/-.004" but is typically
held much closer. The smallest cut possible is dictated by the width of the beam or .008" wide.
Material restrictions – Materials have three factors that restrict them from laser cutting. These
factors are reflectivity, thickness and flammability. Reflectivity causes a problem because the
cutting beam gets scattered. Material that is too thick has the same problem: molten metal
scatters the beam before the part is fully cut. We can cut metal as thick as 3/8" but the edge
quality suffers greatly. The degree of material flammability is another important factor. Some parts
considered flammable can be used. It is best to test flammable or heat sensitive materials before
releasing a production part. Below is a list of some of the material we have used.
Acceptable Materials
• Any raw steel (Stainless, CRS, HRS)
• Aluminum Some deburring issues
• Plastic Check heat & flammability
• Cardstock Check heat & flammability
• Galvanized, Galvaneal
Turret Press Basics
CNC Turret presses are particularly suited for low to medium quantity production runs. By
utilizing “soft tooling” or standard tooling, turrets lend themselves to both the highly flexible
production of prototypes and inexpensive production quantities.
Tolerances – The feature to feature tolerance for the turret press is +/-.004”, the punched hole
tolerance is +/-.002”. When dimensioning for the turret, select meaningful datum in the body of
the part—passing through hole centers, if possible—rather than using an edge or corner of the
part. Edges can be tapered or misaligned and result in enough variance to be dimensionally
uncertain. Furthermore, the use of meaningful datum facilitates inspection.
Special forms – The turret punch press offers many versatile solutions for putting special
features into a flat sheet. Some of the options are counter sinks, offsets, card guides, embosses,
draws, wipe forms, part markings, lettering, lances, half-shears, and weld projections. Virtually
any form can be made as long as it falls within the following constraints. The form depth must be
less than 5/16" and it must fit into a 3.5" diameter circle. Progressive tools can also be made for
the turret press. These tools can punch and form small parts as efficiently as a progressive punch
press tool with a lower initial cost.