3363853 - Introduction - PANELS AND FRAME

SPECIFICATIONS

The following figure shows the underbody dimension specificationsThe comparative dimensions, expressed in millimetres, may vary slightly in relation to those stated, and the mechanic will be able to determine by experience whether this is due to the impact or to manufacturing tolerances.
A. Engine suspension B. Front suspension C. Rear suspension D. Main body reference

SPECIFCATIONS

REPAIRING THE VEHICLE

General safety warnings

The activities connected with repairing the bodywork involve the use of equipment and tools in addition to the handling of chemical products and substances for which the supplier's instructions must be followed.

It is therefore necessary to pay special attention to:

  • The correct use of materials, instruments and equipment: before carrying out any sort of operation, read the instruction manuals carefully and follow the accident prevention and safety instructions with great care.
  • The workplaces for carrying out operations, which should have appropriate ventilation systems which satisfy the legal requirements concerning air exchange, the filtration of harmful substances (solvents) and the reduction of dust levels.
  • The handling of dangerous substances which should be carried out in accordance with the supplier's instructions and recommendations.
The collection and disposal of refuse which should be carried out in accordance with the laws in force.When working with and handling harmful and dangerous substances, the appropriate safety equipment should be employed (clothing, masks, gloves, goggles, etc.).

Vehicle repair operating cycles

The vehicle repair operating cycles usually consist of the following stages:

  • checking the vehicle measurements;
  • cutting/removing damaged elements and preparing the bodyshell for welding;
  • welding replacement elements;
  • preparing for painting;
  • painting;
  • renewing the anti-corrosion treatments;
  • sound insulation, sealants.
Checking and restoring the vehicle measurementsThis is the first stage in the repair process in which the distortion suffered by the bodyshell is measured and evaluated and the components involved are identified.During this stage the first actual repair operation is carried out: pulling the bodyshell to restore the measurements before cutting and removing the damaged elements.Pulling the bodyshellPulling the bodyshell, to restore the measurements, is carried out on straightening benchs where it is possible to secure the bodyshell using vices and attachments which should be fixed according to specific methods for each vehicle, with instructions provided by each supplier.Jigs are used to check the measurements of the bodyshell. They are positioned at specified points, and are used to check the measurements indicated by the jig manufacturer for each model, or alternatively the vehicle's own measurements given in the section 'Descriptions and Operation'.Example of a possible straightening bench configuration.

General repair instructions

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Before carrying out any sort of operation on the vehicle, disconnect the battery terminals.

For safety reasons and for a better quality repair, IT IS PROHIBITED TO:

  • replace structural parts of the bodyshell without using a repair bench. The use of the bench makes it possible to guarantee the restructuring of the vehicle with the original manufacturing measurements, ensuring the correct position of the forecarriage and back-carriage elements.
  • heat the structural parts of the bodyshell to straighten them.
  • cut and weld, edge to edge, any bodywork element and reinforcement on the same line.
Remove the damaged elements, cutting them on the joins, following the cutting lines given in the Service Manual. Carried out correctly, the operation involves wasting a few centimetres between the two cutting lines in order to improve the distribution of the fusible points created by the welding.The diagram below illustrates a possible implementation.
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The removal of the damaged elements is the repair operation during which the potentially most dangerous equipment is used. Before carrying out any operation, read the safety instructions in the manual very carefully and follow the warnings from the manufacturer of the equipment in conjunction with the safety and accident prevention recommendations.

The use of the following is required for the removal of damaged body panels:

  • hack-sawing machines;
  • circular saws;
  • power chisels (only in case of need);
  • plasma-arc cutting systems;
  • electric drills;
  • milling machines;
  • grinding machines;
  • dolly blocks and hammers;
  • disc grinding wheels;
  • air purifiers / extractor systems.
Hack-sawing machineThis type of saw makes it possible to carry out fast and precise cutting, with the possibility of regulating the speed of the blade to suit different situations.Example of the use of a hack-sawing machine
Oscillating circular sawAn oscillating saw is used in cases where high cutting precision is required; for example, when you need to replace the sheet metal of a box section that is laid over a panel which must not be damaged. By adjusting the speed and the number of oscillations it is possible to achieve the precision required according to the conditions of use. The high level of safety of this instrument makes it advisable to use it as an alternative to other types of saws.Example of an oscillating circular saw
Power chisel

A pneumatic chisel is used to remove parts of body panels; it is advisable to use it:

  • when it is not possible to use a power saw, milling machine or drill; for example, when a panel that must not be damaged lies behind the panel that requires cutting;
  • when it is possible to directly separate the welded panels, inserting the power chisel between the two panels along the join edge in order not to leave edges which need removing later on.
The different attachments increase its versatility.Example of the use of a power chisel
Plasma-arc cutting systemThis cutting system, achieved through the combined effect of an electric arc and gas or a mixture of gases, is used whenever it is necessary to cut rather large panels. Depending on the thickness of the panel and the depth of the cut, adjust the current and the gas flow following the instructions in the Manufacturer's booklet.
The use of a plasma-arc cutting system requires the use of an extractor system to get rid of the fumes and harmful gases.
Electric drillAn electric drill is normally used in cases where a milling machine cannot be used; the correct use of the drill to remove spot welds if several panels are superimposed is illustrated in the diagrams below. The attachment to be used in these operations is identical to the one fitted on the milling machine. The spot weld should be marked using a drift, in order to provide a support point for the centring bit, this prevents the drill moving away from the spot and damaging the surrounding area; force should be exerted on the cutter until the depth reached is slightly greater than the thickness of the panel which should be removed (see diagram below).Example of the use of an electric drill
Example of the correct usage of a milling cutter
1. Panel to be removed. 2. Box section panel preventing the use of a milling cutter. Milling cutterA milling cutter for removing weld spots should be used after cutting the panel to be replaced in order to allow the removal of the panel offcuts remaining on the edges of the bodyshell.The milling cutter acts on the panel which constitutes the offcut, cutting it as far as the panel underneath and thereby isolating the spot weld.After the reduction of all the spot welds. the offcut is removed using pliers.To facilitate the operation, use a cutting speed of around 1000 rpm.Adjust the depth of the cutting using the special screw.Example of the use of a milling cutter
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Do not drill matching components. If holes are made by mistake, close them by (MIG) welding. The presence of holes reduces the strength of the component involved and can also give rise to the penetration of water and corrosive agents.
Dolly blocks and leversThese instruments are used when panels need to be straightened by beating, in order to have a counter-action point to support the panel. Dolly blocks are designed so that they adjust to the different panel conformations and, when the working area permits, they can replace a hammer.Levers are used in the same way as dolly blocks, however they are designed so that they can be introduced through restricted openings and spaces to get to areas which are difficult to reach.Dolly blocks and levers are also used to eliminate distortions from the edges of panels which are not removed thereby allowing correct matching with the replaced panels, avoiding weakening the structure.

Welding replacement elements

If welding operations or work which could produce flames near the fuel system components illustrated in the diagram or other flammable parts of the vehicle need to be carried out, the parts involved must be removed from the vehicle and the free pipe connections sealed if the connectors are removed. Disconnect the electronic control units (I.E., ABS, Air Bag, Air conditioning, Alarm, etc.) which could be damaged during the work.Parts of the fuel system

Welding bodywork elements should be carried out, according to requirements, using different methods:

  • Spot welding;
  • Seam (MIG) welding;
  • Brazing.
Equipment

The following equipment is used for these operations:

  • welding guns;
  • seam (MIG) welders;
  • oxyacetylene torches (brazing).
Introduction to electrical spot weldingIn electrical spot welding the heat needed to melt the metal is supplied by the resistance to the current flow provided by the actual metal.Spot welding is carried out to panels where the join edges overlap and the panel metal melts; no metal filler is therefore needed for this type of welding. In areas where three or more panels overlap, spot welding should be repeated for a second time.The type of join produced is not continuous; to create a join with good mechanical strength the spot welds must be correctly spaced following precise instructions (see tables below).Spot welding

In the case of spot welding, check::

  • that the arms are correctly aligned;
  • that the diameter of the edges of the electrodes is correct;
  • the planarity and that the weld edges are correctly matched;
  • that the welding sequence is correct.
Before welding, apply electro-weldable galvanizing protection to the edges of the join to protect the box sections from corrosion.
Spot welder, geometric characteristics of the electrode according to the thickness of the panel and the welding sequence.
A. Electro-weldable galvanizing protective B. Correct welding sequence C. Incorrect welding sequence D. Electrode dimensions Table of reference values for carrying out spot welds.
A. Table for determining the distance of the spot welds from the edges of the panels according to their thickness. B. Table of reference values for the correct spacing of the spot welds according to the thickness of the panel. Do not weld on angular shaped surfaces. Welding on this type of surface would create a concentration of tension which would result in breakage.Example of correct spot welding at corners.
A. Area where welding should not be carried out. Seam (mig) welding

MIG welding should be used for parts where spot welding cannot be used. When carrying out seam (MIG) welding, check:

  • the speed
  • that the seam weld beads have been correctly made (alternating weld sections)
In this welding system (automatic advance seam) a protective inert gas atmosphere is used (hence the name M.I.G. which stands for Met
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