Apple has been getting more aggressive for iPad production in the spring and most of all the summer, suppliers maintained Thursday. Shipments for the tablet are estimated to have doubled to between seven million and nine million iPads in the spring and to jump about 50 percent again in the summer to between 12 million and 14 million. Tips to Digitimes have hinted that Apple has been stockpiling parts all through the spring, such as LG Display's screens, to make sure it won't run short during the summer.