For process engineers and production planners

Tables, calculations and rules for joining plastics, all in one place

We put it together because customers ask us the same things over and over, and because we once hunted for it across ten different sites ourselves. We do not want your email or a registration for it. If it saves you an afternoon of searching, it has done its job.

Send us your part Go to the tables

Stand-alone machines start at EUR 40,000. If you need to weld plastics in smaller volumes, a separate page points you where to look.

What is here

Twenty plastics and how they behave when joined
What welds to what and what does not
Four joint designs with dimensions
Calculations for cylinder force, breaker, air and part weight
Twelve questions for a supplier, and a glossary

Nothing to fill in and nothing to sign up for.

Plastics and how they behave when joined

The twenty most common thermoplastics. The type column is the important one: amorphous plastics soften gradually and carry ultrasound a long way, semi-crystalline ones have a sharp melting point and absorb the energy before it reaches the joint. Almost everything else follows from that.

Swipe the table sideways. On a narrow screen the column with the full name of the plastic is hidden.

Code	Name	Type	Melting or softening	Density	Ultrasonic	Vibration and hot plate	Laser	High frequency	Heat staking
PE-LD	Low density polyethylene	semi-crystalline	105 to 115	0.91 to 0.93	conditionally	yes	yes	no	yes
PE-HD	High density polyethylene	semi-crystalline	125 to 135	0.94 to 0.97	conditionally	yes	yes	no	yes
PP	Polypropylene	semi-crystalline	160 to 170	0.90 to 0.91	conditionally	yes	yes	no	yes
PS	Polystyrene	amorphous	90 to 105	1.04 to 1.06	yes	yes	yes	no	yes
SAN	Styrene acrylonitrile	amorphous	105 to 115	1.06 to 1.08	yes	yes	yes	no	yes
ABS	Acrylonitrile butadiene styrene	amorphous	100 to 110	1.03 to 1.07	yes	yes	yes	conditionally	yes
ASA	Acrylate styrene acrylonitrile	amorphous	95 to 105	1.05 to 1.07	yes	yes	yes	conditionally	yes
PC	Polycarbonate	amorphous	145 to 150	1.20 to 1.22	yes	yes	yes	no	yes
PMMA	Poly(methyl methacrylate)	amorphous	100 to 110	1.17 to 1.20	yes	yes	yes	no	yes
PA6	Polyamide 6	semi-crystalline	215 to 225	1.12 to 1.15	conditionally	yes	yes	conditionally	yes
PA66	Polyamide 66	semi-crystalline	255 to 265	1.13 to 1.15	conditionally	yes	yes	conditionally	yes
POM	Polyoxymethylene	semi-crystalline	165 to 175	1.40 to 1.42	conditionally	yes	yes	no	yes
PBT	Polybutylene terephthalate	semi-crystalline	220 to 225	1.30 to 1.35	conditionally	yes	yes	no	yes
PET	Polyethylene terephthalate	semi-crystalline	250 to 260	1.33 to 1.40	conditionally	yes	yes	conditionally	yes
PET-G	Glycol modified PET	amorphous	80 to 90	1.26 to 1.28	yes	yes	yes	yes	yes
PVC-U	Unplasticised PVC	amorphous	75 to 85	1.38 to 1.45	conditionally	yes	conditionally	yes	yes
PVC-P	Plasticised PVC	amorphous	softens gradually	1.20 to 1.35	no	yes	conditionally	yes	no
TPU	Thermoplastic polyurethane	semi-crystalline	160 to 200	1.10 to 1.25	conditionally	yes	yes	yes	no
EVA	Ethylene vinyl acetate	semi-crystalline	60 to 100	0.93 to 0.95	no	yes	yes	yes	no
PPS	Polyphenylene sulfide	semi-crystalline	275 to 285	1.35 to 1.45	conditionally	yes	yes	no	yes

For amorphous plastics the figure is the softening temperature, not the melting point. They have no sharp melting point and pass into a plastic state gradually. That is exactly why they weld more easily.

Ultrasonic “conditionally” on semi-crystalline plastics means it can be done, but the horn has to come down close to the joint and the joint is better designed as a shear joint, or with a more pronounced energy director.

Laser always needs a pair: an upper part that passes infrared radiation and a lower one that absorbs it. Without the right pigmentation it will not work even on a material the table marks as suitable.

High frequency only works on polar materials with a loss factor of roughly 0.01 and above. PP, PE, PS and PTFE are not among them without special additives.

The figures are indicative ranges for unmodified grades. The exact figure for your material is in the data sheet from your resin supplier. Fillers, flame retardants and colourants all shift them, glass fibre considerably.

What welds to what (and what does not)

The basic rule is merciless: the same material to the same material. Different plastics can only be joined when they are chemically related and their temperature ranges overlap.

Pair	Does it work?	Note
The same plastic to the same	yes	Always the safest route. Even here, though, different grades of the same plastic can differ in flow behaviour.
ABS and PC	yes	They get on well and the temperature ranges overlap. A common and reliable pair.
ABS and PMMA	conditionally	It works, but joint strength tends to be lower than on the same material.
ABS and SAN	yes	Styrene relatives, they hold well.
PC and PMMA	conditionally	Only with careful setting. They soften differently and the joint tends to be brittle.
PP and PE	no	They look similar but they will not join. A classic mistake that shows up only at the trial.
Semi-crystalline to amorphous	no	PA with ABS, for instance. One is not melting yet, the other is already degrading.
Plastic to metal	no	Welding will not do it. The joint is made by heat staking or by pressing in an insert, and there it is routine and reliable.

If you are not sure, send us both parts. We run a weldability trial before the mould is decided.

Joint design: four solutions that cover most parts

The shape of the joint is cut into the mould. Once the mould is finished, every change costs money. That is why it pays to go through it before the mould exists. The dimensions are the usual ranges, the exact figure we confirm against the material and the wall thickness.

Energy director

A triangular ridge on the parting line that melts first and carries the melt into the joint. The most common solution for ultrasonics.

Rule of thumb: An angle of 60° for hard and semi-crystalline plastics, 90° for soft and amorphous ones. Height 0.2 to 0.5 mm, base no more than a quarter of the wall thickness.

Shear joint

The parts slide into each other sideways and the material melts by shear around the perimeter. Used where tightness and strength are needed.

Rule of thumb: On semi-crystalline plastics it is often the only way to a tight joint. It needs a more accurate moulding and a stiffer fixture.

Tongue and groove

The upper part sits in a groove in the lower one. It guides the part and hides the weld.

Rule of thumb: Suitable where the weld must not be visible and where flash would be a problem. It is combined with an energy director at the bottom of the groove.

Heat staking

A plastic stud passes through a hole in the other part and is formed into a head on top. It joins plastic to metal and to a circuit board.

Rule of thumb: The stud should stand one and a half to two of its own diameters above the board. The head overlaps the hole by at least 1.5 mm on each side. The hole has to be chamfered, or the head will not seat.

The most common mistake we come across: a joint designed with no energy director, where ultrasonics is then expected to “join it somehow”. It will not. That comes out at sampling, when the mould is already finished.

Calculations that come in useful when planning

Four things people work out on a calculator every time from scratch. Nothing is sent anywhere.

Force of a pneumatic cylinder

F = p × S

Air pressure bar

Piston diameter mm

This is for the extend stroke. On the retract stroke the rod area takes off roughly ten to twenty percent.

Breaker size and machine current

I = P / (√3 × U × cos φ)

Power input kW

Voltage V

Calculated at a power factor of 0.85. A breaker is sized with a margin, and on machines with heating elements allow for inrush.

Compressed air consumption

Q = consumption per cycle × cycles per minute

Per cycle Nl

Cycles per minute

A compressor is sized with a margin, because other consumers usually hang on the same network.

Weight of a moulding

m = volume × density

Volume of the part cm³

Material

Without the sprue and without flash. It serves to estimate the material cost per piece and to size the handling.

What to have ready in the plant before the machine arrives

The list that usually gets dealt with a week ahead, and then everyone waits for the electrician. The values are typical of machines in the range we supply.

What	Usual value	What to watch
Electrical supply	400 V, 3 phases + N + PE, 16 to 63 A	On machines with heating elements the inrush current is higher than the rated one. A socket or a fixed connection is agreed in advance.
Compressed air	6 bar, dry and filtered	Wet air is the most common cause of pneumatic faults. A separator and a filter always pay for themselves.
Extraction	depends on the technology	High frequency and laser welding need fumes taken away. Ultrasonics usually does not. A high frequency machine also needs screening so that it does not interfere with nearby electronics.
Floor and space	a flat concrete floor	Besides the footprint of the machine, allow room for the operator, for setting parts down and for changing the tooling.
Getting it in	a forklift or a pallet truck	Door height and floor loading. On larger machines this is settled at the time of the order.
Operators	one or two people for training	Training happens at your plant on your part, not on the manufacturer's test piece.

Twelve questions to put to every supplier

Ourselves included. The technical part of a quote tends to look much the same everywhere, the differences only show up here. Print it out and go through it with everyone who sends you a quote.

What control system and what components are inside?Pneumatics, wiring and controls are much the same across European makers. The difference in price is usually somewhere else than the buyer expects.
Who builds the machine, where, and how many of that design have they built?A customer does not want a novelty, they want a proven machine. The number of installations is the only measurable proof. Ask about the manufacturer and the country too: a local site and a local phone number are something an importer has as well.
Can the machine be used for another part and another tool?A machine usually stays for ten years, the product changes sooner. Whether it can take another part decides whether you will be buying again.
What does a second and third tool cost?On products of a similar shape a further tool tends to be a fraction of the machine. Ask before you sign.
What happens if the part fails sampling?Who stands behind the joint meeting your customer's requirement, and what happens then.
Where can I go and see the machine running?A reference visit is the last point before the decision. If it cannot happen at a customer because of confidentiality, there should at least be a visit to the manufacturer.
Where do I buy spare parts and how long do they take?Relays, contactors and switches should be available from a local wholesaler. If they only come from the manufacturer, count on waiting.
What is the service response time and who picks up the phone?Ask for a specific number and a specific person, not for a hotline.
What is the power input, the air consumption and the footprint?Without those you cannot prepare the plant or work out the cost per piece.
Who accepts the machine at the manufacturer before it is loaded?Acceptance before shipping saves an argument about what happened in transport.
Who pays for transport, insurance, installation and training?It tends to be the biggest difference between quotes that look the same.
What is not in the price?The most expensive item in a quote is usually the one that is missing from it.

Anyone who answers one of them evasively is not necessarily a bad supplier. But you know what to ask again.

A glossary for reading quotes and drawings

Quotes for these technologies come in English, German and Czech, and half the misunderstandings start at a single word. There are over sixty terms here, in alphabetical order. You can search in any of the three languages.

Search the glossary

English	German	Czech
amorphous plastic	amorpher Kunststoff	amorfní plast
amplitude	Amplitude	amplituda
blister pack	Blisterverpackung	blistr, průhledný obal
booster	Booster	booster, zesilovač amplitudy
CE declaration of conformity	EU-Konformitätserklärung	EU prohlášení o shodě (označení CE)
clamshell	Klappschale	skořepina
collapse distance	Einsinktiefe	hloubka vnoření
commissioning	Inbetriebnahme	zprovoznění, odladění
compressed air	Druckluft	stlačený vzduch
converter, transducer	Konverter, Schallwandler	měnič, převodník
cycle time	Taktzeit	takt, doba cyklu
die cutting	Stanzen	vysekávání
drawing	Zeichnung	výkres
energy director	Energierichtungsgeber	usměrňovač energie
euro slot	Euroloch	eurozávěs
factory acceptance test, FAT	Werksabnahme	přejímka u výrobce
fixture, nest	Aufnahme, Vorrichtung	přípravek, nástroj
flash	Schweißaustrieb	výronek
forming film	Formfolie	tvarovací fólie
generator, power supply	Generator	generátor
heat staking	Warmnieten	tepelné nýtování
high frequency welding	Hochfrequenzschweißen	vysokofrekvenční svařování
hold time	Haltezeit	doba prodlevy pod tlakem
horn, sonotrode	Sonotrode	sonotroda
hot plate welding	Heizelementschweißen	svařování horkou deskou
laser welding	Laserschweißen	laserové svařování
lead time	Lieferzeit	dodací lhůta
leak test	Dichtheitsprüfung	zkouška těsnosti
leak tightness	Dichtheit	těsnost
lidding film	Deckfolie	krycí fólie
machine footprint	Aufstellfläche	půdorys stroje
manual loading	manuelle Beschickung	ruční zakládání
mould, tool	Werkzeug, Form	forma
moulded part	Formteil	výlisek
number of cavities	Kavitätenzahl	násobnost nástroje
operator training	Bedienerschulung	zaškolení obsluhy
parting line	Trennebene	dělicí rovina
peelable lidding film	Peelfolie	odlupovací fólie, peel
peelable seal	Peelverschluss	odlupovací uzávěr
plastic welding	Kunststoffschweißen	svařování plastů
power input	Anschlussleistung	příkon
purchase contract	Kaufvertrag	kupní smlouva
push-through pack	Durchdrückpackung	protlačovací obal
resealable pack, peel and reseal	wiederverschließbare Verpackung	obal, který jde znovu zavřít
rotary indexing table	Rundschalttisch	otočný stůl
safety guarding	Schutzumhausung	ochranný kryt, oplocení
sampling, PPAP	Bemusterung	vzorkování
scrap rate	Ausschussquote	zmetkovitost
semi-automatic machine	Halbautomat	poloautomat
semi-crystalline plastic	teilkristalliner Kunststoff	semikrystalický plast
shear joint	Quetschnahtverbindung	střižný spoj
site acceptance test, SAT	Abnahme beim Kunden	přejímka u zákazníka
spare parts	Ersatzteile	náhradní díly
spin welding	Rotationsschweißen	rotační svařování
stroke	Hub	zdvih
tensile test	Zugversuch	zkouška tahem, trhací zkouška
thermoforming	Thermoformen	termoformování
thermoplastic	Thermoplast	termoplast
tongue and groove	Nut und Feder	pero a drážka
ultrasonic welding	Ultraschallschweißen	ultrazvukové svařování
vibration welding	Vibrationsschweißen	vibrační svařování
warranty	Gewährleistung	záruka
weld time	Schweißzeit	doba svařování
weld, weld seam	Schweißnaht	svar
welding force	Schweißkraft	přítlačná síla

Is a term you ran into in a quote missing here? Send it to info@tp-t.cz and we will add it.