Table Of Contents
3.0Product
3.1Introduction Of General Press And Die Requirements
3.2Types Of Hems
3.2.1Modified Flat
3.2.2Flat
3.2.3Rope
3.2.4Partial
3.2.5Downstanding
3.3Product Design Requirements (Steel)
3.3.1Typical Flat Hem Sections for Steel Closure Panels
3.3.1.1Flat Hem Straight Section (Steel)
3.3.1.2Flat Hem Concave (stretch) Section (Steel)
3.3.1.3Flat Hem Convex (shrink) Section (Steel)
3.3.1.4Flat Hem Character Line Section < 40 mm Width (Steel)
3.3.1.5Flat Hem Character Line Section >= 40 mm Width (Steel)
3.3.1.6Flat Hem Corner Section (Steel)
3.3.1.7Flat Hem Laser Weld Joint Section (Steel)
3.3.2Typical Rope Hem Sections for Steel Closure Panels
3.3.2.1Rope Hem Radius Requirement
3.3.2.2Rope Hem Straight Section (Steel)
3.3.3Decklid - Single Piece Outer (Steel)
3.3.4Door (Steel)
3.3.
4.1Door - Cargo (Steel)
3.3.
4.2Door, Front - Door-Into-Roof (Steel)
3.3.
4.3Door, Rear - Door-into-Roof (Steel)
3.3.
4.4Door, Front - Frame-Under-Glass (Steel)
3.3.
4.5Door, Rear - Frame-Under-Glass (Steel)
3.3.
4.6Door, Front - Headerless (Steel)
3.3.
4.7Door, Rear - Headerless (Steel)
3.3.
4.8Door - Sliding (Steel)
3.3.5Endgate (Steel)
3.3.6Hood (Steel)
3.3.6.1Hood (Steel)
3.3.6.2Hood - Clamshell (Steel)
3.3.6.3Hood - With Headlight Cutouts (Steel)
3.3.7Liftgate (Steel)
3.3.8Rear Access Panel (Steel)
3.3.9Roof (Steel)
3.3.9.1Roof - 2-Sided Hem (Steel)
3.3.9.2Roof - 4-Sided Hem (Steel)
3.4Product Design Requirements (Stamped Aluminum)
3.1.4Typical Rope Hem Sections for Aluminum Closure Panels
3.4.1.1Rope Hem Straight Section (Aluminum)
3.0 Product
3.1 Introduction For General Press And Die Requirements
The purpose of this report is to attempt to understand, summarize, and
explain all of the hemming recommendations that have been assimilated
by General Motors. Many of these recommendations can be generalized
across vehicle platforms. All sketches in this document are not to scale
and do not represent a specific product design. They are used to
express concepts and ideas only.
3.1.1 Hem Press and Die Basics
Understanding basically how the hem press works may allow
significant cost savings through design for manufacturing. The
outer panel is located up/down and fore/aft for side closures (cross
car and fore/aft for front and rear closures) by several small blades
(usually 2 per side). Relief for the locator blades must be provided
in the lower die, the pre hem steels, and the final hem punch.
Sometimes a block will be used in the handle pocket to better
locate the outer panel. The cross car for side closures (up/down for
front and rear closures) location is controlled by the lower die. As
the ram on the press is lowered, the inner panel is located fore/aft
and up/down for side closures (cross car and fore/aft for front and
rear closures) by gauge pins in the spider. The gauge pins are
slightly undersized to the holes. The hole surfaces should be
perpendicular to the pins. A full periphery blade holds the inner to
the outer, while blocks locate the 'S' surfaces on the inner panel,
~
2 per side
The hem press generally uses a cam operation for pre hem and a
full periphery anvil for final hem. Individual product design may
require the final hem to be a cam operation. The target maximum
for direct hemming is 60° (70° is the highest ever achieved). If the
product design requires the panel to be tipped too far, a cam is
used for the final hem.
direct final hem cam final hem
3.1.2 Pressure Pad
The hem press utilizes a full periphery pressure pad. This pad
serves a variety of functions throughout the hemming operation. It
helps to ensure a high quality hem by holding the inner to the outer
panel, and it prevents the panels from slipping within the die.
Panels must be designed to allow room for the full periphery pad. It is preferred to have 6.0 or 7.0 mm to package the pressure pad
around the periphery of the door.
overflanging of the outer panel should be considered when
designing these sections. It is also important to consider the detail
outer panel hem flange trim line. This trim line must be controlled
due to the tight condition between the trim line and the full
periphery presser pad.
leading edge of door
bottom edge (sill) of door
barrier flange of door
The pressure pad is commonly relieved to allow https://www.doczj.com/doc/d314013760.html,ually, a 1:4 ratio is used to determine the allowable relief.3.1.3 Determining the Panel Tip Angle
Ideally, the hem press centerline is aligned with the detail outer panel die datum lines. The same up/down and cross car die datum lines should be used for both front and rear doors. This helps to reduce complexity and allows easy part transfer into and out of the hem press.
Ideally, the press direction should be perpendicular to the inner panel surface. This allows the upper ram to accurately locate the
inner panel to the outer panel using the inner panel gauge holes. Some accuracy may be sacrificed if the inner panel is tipped. This
for hemming. This issue must be studied for every specific product design. A list of a few general items that may force a change to the panel tip angle includes:
1. A small wall angle (less than 3°) when measured to the body
gridlines at the beltline or at a recessed molding area.
2. Over 30° of curvature at the belt.
3. Over 30° of curvature at the sill.
All three of the above conditions are important. A balance between all three must be found and the optimum tip angle decided. Usually the beltline is considered most important, feature lines and recessed molding areas secondary, and the sill area least important for hem quality.
A good example of a case where the tip angle had to be changed is the '97 C car design (see next page). The angle of the beltline was originally -8° from the body grid line and the angle of the door at the sill was 15°. The panel had to be tipped 11-12° to allow 3-4° for hemming at the beltline and sill.
In general, an open angle of 7-8° is required for direct hemming. An open angle of 3-4° is required for cam hemming. Any open angle below 3-4° may result in difficulty loading and unloading the panels. A separate pre-hem station or second hem press may be required. The same rules apply to other areas of the door such as the feature lines or recessed molding areas. Each design must be analyzed on an individual basis.
3.3.1.7 Flat Hem Laser Weld Joint Section (Steel)
(information not available at this time)
3.3.2 Typical Rope Hem Sections for Steel Closure Panels
3.3.2.1 Rope Hem Radius Requirement
(The information below is a place holder at this time. A
possible link to existing export requirement information will
be investigated.)
Hem radius (for European vehicles): R ≥ 2.5 mm for
protruding portion of hem if gap between hem edge and
adjacent edge or surface (e.g. windshield) is > 40 mm.
Refer to European Council Directive 74/483/EEC for
complete specification.
3.3.3 Decklid – Single Piece Outer (Steel)
3.3.4 Door (Steel)
3.3.
4.1 Door – Cargo (Steel)
3.3.
4.4 Door, Front – Frame-Under-Glass (Steel)