What is the welding fixture

The welding fixtures are usually made of high-strength materials and can withstand the heat and mechanical stress generated during the welding process.

Their structures are diverse, ranging from simple fixture blocks to complex combined fixture systems. They are customized according to specific welding requirements.

In the manufacturing industry, Welding fixture is a widely used type of tool, and there are numerous varieties, take welding fixtures of automotive as an example.

It’s a special tool that used to production of body-in-white during the assembly and welding , make sure the correct position and clamp the metal parts, ensuring welding accuracy and assembly part quality.

 

       

 

What is the function of welding fixture

a. Guarantee Dimensional Accuracy

Ensure after the body-in-white welding to retains correct geometric shape and size, make sure such as door, hole etc complete match the design requirement, improve overall body-in-white quality and assembly precision.

b. Improve Production Efficiency

Realized automated assembly line, raise assembly productivity for assembly and welding, reduced the workload, reduced the manufacture cost.

c. Control Welding Distortion

Prevent the part distortion during the welding, make sure all the welding beam position of part and adjust them to the best position, mitigate the welding stress and distortion to make sure the body-in-white quality.

What is the work flow of welding fixture

a. Cylinder open

b. Location and upload the part

c. Cylinder clamp well

d. Welding

e. Take off the part

What is the welding fixture design requirement 

a. To ensure the CMM report received is comply with OEM standards, product must be fixed in-car position, this only applies to welding fixture where the main portion of the product is present to be welded. All other sections of sub tooling should have their respective products positioned within their own sub assemblies.

b. Each welding fixture will require teach pin that can be rotated between CMM bushing, this is to help programmers establish the taught positions of robot.

1. Welding considerations

a. Tooling should be designed so that there is sufficient clearance around the welding gun or welding torch (at least 10mm in all directions) to access all welding locations, along with the following guidelines:

• Accounting for tip wear and open position of the spot weld gun
• (Spot welding) with gun electrodes perpendicular to product surfaces
• (MIG welding) with torch at an angle roughly between 30°-45° to welding surfaces
• (MIG welding) with torch roughly at a 5°-15° push angle

2. Quality requirement

a. Welding fixture is designed in way to adhere to the supplied process including ,any dump or manual tooling, desired loading sequence and product orientation.

b. Net and pin locations used in design should match-or in the case of nets be in the general position – of the location indicated on the supplied datum scheme

c. Must include a sensor for every component in the assembly, including nuts and studs that are newly introduced in the process

d. Require detection for an unfinished welded sub assembly that is loaded from a previous welding fixture

e. Welding fixture is designed in a way to prevent the ability to load incorrect or similar components into any area of the tooling

f. Welding fixture designed in a way to prevent the correct component from being loaded in more than one orientation

h. In the case where tooling is be manually changed over, or swapped out in place of other tooling accommodate different models of the product,there must be a means included to poka-yoke the multiple required tooling.

3. Ergonomic considerations

a. Working height of the operator mush be kept at 33.9″ to 49.4″ and no more than 25.8″ measured from the back of the shoulder blade.

b. This ” working height ” also includes tooling that impedes the operator’s ability to load/unload within the specified limits

What is the welding fixture mechanical section requirement 

1. Clamps and Cylinders

a. Provided a list of approved components

b. Acceleration or deceleration of pneumatic controlled mechanisms must be done with flow control valves

c. Hydraulic shock absorb may be required to avoid damage to parts and tooling, distance the tooling will travel and its mass need to be considered

d. All camps and cylinders will be checked for open or closed status

e. Clamps, Cylinders and /or Tooling that must be held in a position to prevent hazard that may cause injury must have a method of mechanically locking into any given position, in all cases such as described above, a rod locking mechanism is the general considered the preferred solution

f. The locking method must be designed that in the event of an Emergency Stop the tooling /cylinder/clamp in question must be stopped immediately and locked from movement

h. In general hazards must be identified in a risk assessment to determine what level of safeguarding is required to control the hazard.  In the event that the hazard being controlled could cause very serious injury the risk assessment will determine if redundant locking methods must be used

l. If ball plungers are used they mush be accompanied by a hardened contact surface (minimum hardness of 52 HRC) for the ball to engage with

m. P.O checks to be reviewed and approved by customer on a case by case basis

n. Center closed valves are not considered an acceptable solution to hold tooling subject to forces of gravity , final design of items of this nature must be approved by customer.

 

2. Tooling driven by clamps, cylinders and other forms of automation

a.  All tooling driven by pneumatic, hydraulic or electrical force, for the purpose of clamping product against a net pad must be made as follows

• Material： A2 tool steel or Namms NC Blocks
• Hardness: ROCKWELL C58-62
• Exceptions are as follows – Parts within a weld loop need to be non-magnetic stainless steel

– When within 100mm of MIG welding and not protected from spatter material needs to be Ampco 18

b. All tooling driven by clamps, cylinders or other forms of automation must be adjustable, in the direction perpendicular to the contact surface where such tooling meets, care must be taken to ensure side-loading of clamp, cylinder or other form of automation is kept to a minimum

c. Rocker clamps may be used to reduce clutter but the following points must be considered

• Two points of contact
• Designed in such a way to prevent product from becoming damaged due to sharp edges
• Control the rocking ability of the clamp piece to effectively apply equal pressure to both targets
• Mounting sensors to rocker clamps should be avoided wherever possible

 

3. Pins

All pins made as follows :

If pin is greater than 6mm diameter

Material : A2 Tool steel or NAAMS locating pins

Hardness : ROCKWELL C 58-62

If pin is less than 6.0mm diameter

Material : S.A.E. 4140, pre-hardened, no-post treatment

 

4. Nets

All net surface made as follows:

Material : A2 Tool steel or NAAMS NC Blocks

Hardness: ROCKWELL C 58-62

 

5. Shims

All aspects of adjustability must be done with the use of shims, metric sizing between 0.25mm to 2.0mm – NAAMS type coated to prevent rust

 

6. Grippers

a. At least 2″ of clearance is needed past the opening of the cow’s mouth to all for robot cable/hose bundle

b. If the gripper is larger than 3.5′ in one direction, there must be a means of easy transportation

c. For all grippers, there must be a insulation kit provided to rest between the EOAT and the cow’s mouth of the robot

What are most components  of welding fixture

Overall structure

1. Base and supporter

It’s ensure overall rigidity, horizontal reference, bearing all positioning elements, tightening components, including base, supporter, L-shaped adapter angle seats, and leveling anchor bolts.

2. Positioning Limiting Module

Locator pin : limiting part hole position, make sure XYZ datum;
S shape block and supporter : Touch part shape to support part
Limiting stopper : Prevent parts from being out of position, flipping, and incorrect assembly
Poka Yoke pin: Prevent the wrong installation of part, otherwise the equipment will not be able to start the welding process.

3. Activate the acceleration execution module

Rotary clamping cylinder / Lever cylinder: Clamping power source
Clamping arm, pressing head: Directly press the sheet metal, preventing it from slipping
Cylinder pneumatic unit: pressure regulation, filtration, and lubrication for the cylinder
Buffer stop block: Limits the travel of the clamping arm to prevent damaging the part

4. Auxiliary Signal Matching Module

Position detection proximity switch: Detects whether the part is placed in the correct position and whether the clamping arm is securely pressed.
Piping and solenoid valves: Uniformly control the opening and closing of all cylinders
Routing channels, protective baffles: Protect the pipelines and prevent welding splashes

 

The welding fixture, base on a steel base plate,it is equipped with positioning pins and  support blocks to precisely position the part.
The part is automatically clamped by the cylinder and the clamping arm. The PLC is linked with the sensor switch and pneumatic components to achieve stable and automatic clamping.