Apple CEO Tim Cook warned us that there would be a significant shortage of new iMacs when they launched in October, and that shortage seems to be continuing, with 21.5in models showing dispatch estimates of 7-10 days, and 27in with shipping delays of up to four weeks.

A new report from DigiTimes suggest that these shipment delays are due to mass production issues that are preventing Apple from being able to make its 27in iMacs fast enough.

According to the report, industry sources have said that the mass production issues are being faced by Apple's panel supplier, LG Display, which is believed to be experiencing problems with the lamination process when making panels for the new iMac. SEE: Apple iMac (Late 2012) review

These issues are thought to have slowed down shipments of the 27in iMac to 100,000 units a month, say DigiTimes' sources.

The 21.5in model is experiencing less trouble, with LG Display managing to secure strong yields of the smaller iMac at around 300,000 to 400,000 units of the computer shipping per month, DigiTimes reports.

The 27in iMac's shipment delays are expected to ease in February, when DigiTimes' sources say LG Display will begin harnessing better yields for its panels.

The lamination process for the new iMac's screen was first identified as a challenge by KGI Securities analyst Ming-Chi Kuo in August last year, who noted that the new screen lamination process for the redesigned iMac is more difficult with the 27in model, and suggested that as a result it would launch six to eight weeks after the 21.5in option. This prediction later proved to be true.

This week, Apple introduced the Fusion Drive upgrade for new entry-level 21.5in iMac orders, an option previously only available for high-end and 27in iMacs.

See also:

New 2013 iMac could ship next spring

Lab tested: Our review of the 2012 iMac with Fusion Drives, CPU upgrades