How to request a plastic injection moulding quote and which details drive the price

To assess a plastic part, we need to know what has to be made, in what material and in what quantity. If any of these is missing, it has to be assumed, and an assumption may not match what you need.

Here we explain what information to gather for an injection-moulded or blow-moulded part and how each item affects the price. We manufacture by injection moulding and blow moulding at our factory in Tibi (Alicante). Our injection moulding machines range from 100 to 500 t of clamping force. You will find a checklist at the end.

A university plastics textbook works out the cost of an injection-moulded part item by item^{Source 1}. These are the main items that depend on your part, and they explain why we ask for each piece of information.

• Material, based on the part weight, the scrap (the material lost along the way) and the price of the plastic and its additives^{Source 1}.
• Mould, whose cost can be spread across the parts. If the customer supplies their own mould, that share is not included in the price^{Source 1}.
• Machine, the hourly rate of the injection moulding machine divided by the number of parts it produces in an hour^{Source 1}.
• Secondary operations, such as assembly, drilling or machining, with their time and their rate^{Source 1}.
• Packaging, which is a product cost, and transport only if the price includes it^{Source 1}.

The cycle is the time the injection moulding machine takes to produce one shot of parts. A large part of that time goes into cooling them until they can withstand ejection^{Source 2}. In the cooling equation, thickness is squared, which is why it is the most influential factor^{Source 2}. With the same material and the same temperatures, a wall twice as thick takes around four times as long to cool. If a thick section serves no function, it is worth reviewing it before the mould is made.

Start with the 3D model in a neutral format, one that can be opened in software other than the program that created it. One of the most widespread is STEP (ISO 10303-21)^{Source 3}, designed for exchanging product data between computer systems^{Source 4}. IGES is another neutral option for exchanging the definition of a part between design and manufacturing software^{Source 5}.

The 3D model alone may not be enough. For years, the shape was sent in STEP AP203, one of the most widely used application protocols alongside AP214^{Source 4}, and the dimensions and tolerances were copied by hand from the drawing^{Source 3}. AP242, published in 2014 to replace the earlier protocols, can carry them within the file^{Source 3}, provided the recipient can read them. That is why it is worth adding a 2D drawing in PDF, which will also be the reference for approving the samples^{Source 6}. It should include the following.

• The critical dimensions, each with its tolerance, for example the diameter where a shaft fits or the distance between two fixing points.
• The material and its grade, or the requirements it must meet.
• The finish of each visible surface and the areas where no mark is allowed.
• The drawing number and its revision, so that everyone is working from the same version^{Source 1}.

The plastic and its specific grade should be clearly stated from the very first enquiry^{Source 1}. The same plastic is sold in different grades, with higher or lower flow or with glass fibre, which are processed differently^{Source 7,Source 8}.

The material affects the price through its cost per kilo and through its processing. Some plastics absorb moisture and must be dried before moulding^{Source 7}. Each plastic shrinks by its own amount as it cools, known as shrinkage, and the mould cavity is enlarged according to the material’s nominal shrinkage^{Source 9}. That is why a mould designed for one plastic may not give the same dimensions with another.

A colder mould shortens the cycle, within the limits of each material^{Source 11}. If you have not yet chosen the plastic, tell us what the part is for, what temperature it will operate at, whether it will be exposed to sunlight or come into contact with food, and what loads it must withstand.

The relatively high cost of the mould is one of the major drawbacks of injection moulding^{Source 1}. To spread that cost over the price, the number of parts the mould will produce has to be estimated, and each part carries the mould cost divided by that total quantity^{Source 1}.

So the cost per part can be summed up as two components: a variable cost, which includes the material and machine time, and the mould cost divided by the total quantity^{Source 1}. In the figure, each column is that sum for a given total quantity, which doubles from one column to the next, and you can step through them with its control.

Workshop bench with a closed injection mould topped by a cycle counter, a pallet with a box full of parts beside it and, on the right, eleven columns in front of a ruled board, one for each doubling of the total quantity, from 1,000 to 1,024,000 parts. Each column is the cost per part: a light block, the same in every column, which is the variable cost, topped by a steel sheet, which is the mould share and measures half as much in each column as in the one before. The row drops quickly and then levels off at the height of the variable cost. A carriage on the edge of the bench points to the column for the chosen total quantity, tinted green, at first the one for 1,000 parts, where the mould share is eight times the variable cost. As you step through the quantities, the counter turns and the stack gains a box each time the total quantity doubles. It is the same single-cavity mould for every quantity and the units are relative: the variable cost of one part is 1, and the mould costs as much as the variable cost of 8,000 parts.

The cost per part falls as the total quantity rises^{Source 12}. The columns drop quickly and then level off, because the mould share becomes small compared with the variable cost.

It helps to give the forecast by week, month and year, with the demand peaks, and to say how much stock you can store^{Source 12}. The batch size, the number of parts in each run, also counts. Each run carries a mould changeover cost and a trial material cost, which an injection moulding cost estimation system divides by the parts in the batch^{Source 13}, so it weighs more heavily on a small batch.

A cavity is each recess in the mould that produces one part per cycle. In the textbook example, the lowest cost per part is achieved with 2 cavities for a total of 200,000 parts, with 4 for 400,000 and with 8 for 800,000^{Source 12}. It is an example, not a rule.

Generally, more cavities mean more variation between parts, and the required precision limits their number^{Source 12}. Another limit applies when the mark left by the gate, where the plastic enters, must not be visible^{Source 12}. According to the textbook, with a cold runner a second cavity costs around 60% more than a single one, and with a hot runner, 100% more^{Source 12}. We explain these systems in our article on types of injection moulds.

Colour is affected by the plastic, the additives, the texture, the shape, the lighting, the environment in which it is used, the process and, above all, the person looking at it^{Source 14}. A colour chart code is a good starting point, but it may not be enough.

It is best to send a physical sample in plastic. A paper, paint or fabric sample can lead to a mismatch due to metamerism when it is matched with a masterbatch, the pigment concentrate that is mixed into the plastic^{Source 15}. Metamerism occurs when two colours that match under one light no longer match under another. It happens because the two samples reflect each region of the spectrum differently, and since each light source distributes its energy differently, the difference shows under some lights and not under others^{Source 15}.

Add the end use and the applicable regulations, which may restrict the choice of pigments^{Source 15,Source 14}, along with the material, the thickness, the texture, the light under which the colour will be assessed and the colour difference you can accept. These are, among others, the details a colour concentrate manufacturer asks for to match a shade^{Source 14}.

The concentrate counts towards the material cost according to its dosing rate, 1% in the textbook example^{Source 1}. We explain how a colour difference is measured and toleranced in our article on colour measurement in plastics.

A tolerance is how far an actual dimension may deviate from the one shown on the drawing. The international standard on tolerances for moulded plastic parts is ISO 20457:2026, the second edition, published in August 2026, which replaces the 2018 edition^{Source 16}. It exists because plastic varies more than metal due to shrinkage, warpage and uneven cooling, and in general the criteria used for metal cannot be applied as they stand^{Source 16}.

It lists injection moulding, injection-compression moulding, transfer moulding, compression moulding and rotational moulding, and applies to other processes only if the contracting parties agree^{Source 17}. Blow moulding is not on that list. In Germany, DIN 16742:2013 gave way to DIN ISO 20457, the German version of ISO 20457:2018, with the same classification principle^{Source 18}. If your drawing still cites DIN 16742, it is worth reviewing the move to ISO 20457:2026 with your supplier, because the standard on the drawing sets the tolerances and the acceptance conditions^{Source 16}.

The part reproduces the surface of the cavity, more or less faithfully depending on the mould temperature^{Source 2}, so the finish is decided mainly in the mould. For surfaces produced by spark erosion (EDM), a machining process that uses electrical discharges, the VDI 3400 guideline groups roughness into grades from VDI 00 to VDI 45, a scale used worldwide for moulds^{Source 19}.

A texture calls for a larger draft angle, the taper of the walls that allows the part to be released from the mould. As a guide, 1 to 2 degrees is allowed, plus at least 1.5 degrees for every 0.025 mm of texture depth, so a 0.125 mm leather texture adds at least 7.5 degrees to the normal draft^{Source 20}. The guidelines for each texture are provided by its suppliers or by mould makers^{Source 20}.

Before series production, the mould goes through several trials. They are usually named with a T and a number, and the last one is known as Tf^{Source 6}. These are generally names used in practice rather than defined by a standard, so it is worth agreeing what each one includes.

1. First trial, to check that the mould works. If it goes well and samples are already being produced, it counts as the first sampling trial^{Source 6}.
2. First samples, which may not yet have the final dimensions or surface^{Source 6}.
3. Dimensional report covering all dimensions, known as first article inspection^{Source 6}.
4. Corrections to the mould wherever the part does not match the 2D or 3D data^{Source 6}.
5. Texturing or polishing, once the dimensions are confirmed. Together with their moulding trial, they can take up to a week^{Source 6}.
6. Final trial under conditions that simulate series production, which ends when its samples are approved^{Source 6}.

This phase can cause serious delays to a project^{Source 6}. That is why it is worth stating the date by which you need the first parts and series production, and whether there is a fixed date behind it, such as a product launch.

When the mould already exists, the first step is to check that it fits the injection moulding machine that will run it.

• Clamping force. The force required increases with the injection pressure and with the projected area of all the cavities together, the area they cover when projected onto a single plane, which for each part corresponds to its widest outline^{Source 21}. The injection moulding machines at our factory range from 100 to 500 t, and we explain that figure in the quality section.
• Size. The mould must fit between the machine’s tie bars, and the machine must open far enough to mount the mould, open it and eject the part^{Source 21}.
• Shot size. The injection capacity must be in proportion to the part, because plastic that stays too long in the barrel can degrade^{Source 11}.

When a mould moves from one moulder to another, it is worth inspecting it with its owner on receipt and gathering its dimensions, its weight, its water and hydraulic connections, and the times, temperatures and materials it used to run with^{Source 22}.

If the part will come into contact with food, Regulation (EU) No 10/2011 applies in the European Union^{Source 23}. It establishes a Union list of authorised substances and sets, as a general rule, an overall migration limit, the amount the plastic may release in testing, of 10 mg per dm² of contact surface^{Source 23}.

At marketing stages other than retail, there must be a written declaration of compliance. Among other details, it states which foods the part may be used with, the time and temperature of contact and the highest surface-to-volume ratio for which compliance has been verified^{Source 23}. So, for a food-contact part, it is worth stating which foods it will be in contact with, at what temperature and for how long.

If it will be used outdoors, tell us that too. Degradation by ultraviolet radiation from the sun is perhaps the most important form of environmental degradation in plastics. Its effect varies greatly from one plastic to another, and it is countered with additives that absorb that radiation, the most common of which is carbon black^{Source 24}.

Blow-moulded parts are hollow by nature^{Source 25}, like bottles, and we explain how they are made in the technology section. Almost all of the information above applies to them, with a few differences.

Blow moulding is not a particularly precise process, although injection blow moulding, which starts from an injection-moulded part, allows considerably tighter tolerances than extrusion blow moulding^{Source 25}. Wall thickness varies because of the process itself^{Source 25}, so state the minimum you need and where. Since ISO 20457 does not list blow moulding, its tolerances apply only if agreed^{Source 17}, so it is best to set them on the drawing. And if the thread is formed during blowing, it should have a coarse pitch and allow for considerable variation^{Source 25}.

This table summarises the main information. You do not need all of it to request a quote.

There is no single figure. One estimation method adds up the machining hours for each part of the mould and multiplies them by a rate^{Source 12}. The price rises with the number of cavities and with a hot runner^{Source 12}, and ranges from prototype moulds, the most economical, to very high-production moulds, the most expensive^{Source 26}.

Normally it belongs to the customer^{Source 1}. Even so, it is worth putting this in writing in the order, especially if its cost is spread over the price.

If you have a part in mind, we will review it with you using whatever information you already have. A member of our team will look after you, with a 100% human service, from the first call through to delivery. We manufacture in Tibi with semi-automated processes and less than 1% of parts returned. Call or write to us and tell us what you need. You will find more short answers in the frequently asked questions on our home page.