Pallet Manufacturing Process - Modular pallet design

Pallets are widely used all around the world in diﬀerent sectors to transport goods over short distances or for storing. Conventionally the pallets were made from wood, but over a period of time with advancements in technology and material researches they are made with variety of materials. In general, it could be said that they are made from plastic. The reason to use plastic is that it is cheap, strong, light weight, durability, could be used in diﬀerent environments and could be easily recycled. Another great advantage being that it can be made in any complex geometry as required for a particular purpose. The wooden pallet has basically one major manufacturing process, in which the wood is sliced in strips/

Weightage

Concept C-1 C-2 C-3 C-4 C-1 C-2 C-3 C-4 C-1 C-2 C-3 C-4 C-1 C-2 C-3 C-4 C-1 C-2 C-3 C-4

Stability 5 5 1 2 4 5 2 5 4 5 2 5 4 5 1 3 4 5 2 4 4

Ease of use (operator &

Cartesian system0 3 5 2 1 4 5 4 2 5 4 2 3 5 5 3 4 5 5 3 3 5 Compatibility (different sizes of discs) 5 1 5 5 3 3 4 3 5 5 5 3 5 3 5 3 5 3 5 4 5 Robustness 4 5 3 1 5 5 2 5 4 5 2 5 4 5 2 4 4 5 2 4 4 Manufacturing & Maintenance Feasibility 3 4 1 5 4 3 2 2 4 2 3 3 5 2 1 2 3 3 2 3 4 Total Score 77 51 57 79 84 56 72 88 88 58 78 91 81 50 64 85 83 58 74 88 Aggregate Parameters

blocks of desired thickness and the joining is done with fasteners like nails, screw, etc. On the contrary there are variety of processes that are used to produce a plastic pallet, some of which are listed below and elaborated further. Key manufacturing processes:

1.

Injection moulding

2.

Thermoforming

3.

Blow moulding

4.

Compression moulding

5.

Rotational moulding

6.

Profile extrusion I. INJECTIONMOLDING

It is one of the most popular processes of shaping plastics to a desired shape and size. This process is best suited for large scale production sizes, especially where the same design has to be produced several times. Generally, injection moulding process involves the following key steps:

 Raw material is fed into the machines through a hopper.  Heater bands and frictional force melts the plastic material.

 Hot plastic in liquid state is injected with a nozzle into the mild cavity, where it cools and hardens. Two Types of injection moulding are possible

-Low Pressure Structural Foam Moulding: The mould cavity is injected with plastic pallet material and an inert gas. Heating a mixture of nitrogen gas and polypropylene activates blowing agents. This produces a cellular core surrounded with a rigid plastic material.

-High Pressure Injection Melding: Used for high-density polyethylene (HDPE) plastics. It is a precise process and requires no/minimum post processing

II. THERMOFORMING

The plastic is heated to a pliable temperature then it is formed over a mould and allowed to cool. Thermoforming plastic pallet is a three-step process that involves:

 Heating the plastic pallet material; this results in an extruded plastic sheet with a desired thickness.  Forming either one or two sheets against the mould, while evacuating air between the sheet and the

mould. Alternatively, a vacuum suction draws and pushes the heated plastic onto the mould.  Allow the formed plastic pallet to cool.

Two types of thermoforming techniques are quite popular:

Vacuum Thermoforming: The plastic pallet is made into desired shape using heat and pressure. The heated plastic material is put over a mould and then it is drawn into the mould by a vacuum. -Pressure Thermoforming: Similar to the vacuum thermoforming. However, in addition to the force/pressure generated by the vacuum, an extra pressure is applied that will force the plastic into the mould.

Good for aesthetic qualities, i.e., it can create greater detail such as textured surface, undercuts, sharp corners, etc. Slow cycle time and cheaper process as compared to injection moulding.

III. BLOWMOLDING

Blow moulding is used for forming hollow parts. The key stages are:  Melt the plastic material.

 Forming into a tube-like piece of plastic that has a hole on one end where compressed air can pass.

 Clamp the hole into a mould.

 Blow air in to expand it to take the exact shape of the mould.  Allow it to cool and harden.

Parts made from blow moulding don’t get damaged easily and show very little or no damage when accidentally hit by a forklift. Have excellent resistance to impact compared to injection moulded plastic pallets.

IV. COMPRESSIONMOLDING

This a cost eﬀective process as compared to injection moulding. Requires low cost of tooling and labour besides, the process minimizes wastage. The process of manufacturing:

 Material is placed into a desired mould

 Meld is heated as a predetermined amount of pressure is applied.  The pressure is maintained until the pallet cures.

Slow process compared to the injection moulding technique.

V. ROTATIONALMOLDING

In this process the plastic materials are ground into small pieces such as powder or granules. Later this is loaded into mould and sealed, heated and rotated in two perpendicular axes. The centrifugal motion assures that every particle is mixed and distributed within the mould. After the pallet can be removed, once the mould cools down.

VI. PROFILEEXTRUSION

 The plastic pallets made from this process mainly resemble wood pallets.  The plastic is melted and forced through an extruder.

 The extruded profile is cut to diﬀerent sized parts/shapes.  Later these are fastened together using nails, heat or welds.

Incorporating fasteners will make the pallet unsafe unlike those made from other processes.

Depending on the production capacity, application and design of a plastic pallet a suitable production process has to be opted.

In document Modular pallet design (Page 52-54)